This PR fixes #7598 by providing a configurable way of signing commits across the Gitea instance. Per repository configurability and import/generation of trusted secure keys is not provided by this PR - from a security PoV that's probably impossible to do properly. Similarly web-signing, that is asking the user to sign something, is not implemented - this could be done at a later stage however.

## Features
- [x] If commit.gpgsign is set in .gitconfig sign commits and files created through repofiles. (merges should already have been signed.)
- [x] Verify commits signed with the default gpg as valid
- [x] Signer, Committer and Author can all be different
    - [x] Allow signer to be arbitrarily different - We still require the key to have an activated email on Gitea. A more complete implementation would be to use a keyserver and mark external-or-unactivated with an "unknown" trust level icon.
- [x] Add a signing-key.gpg endpoint to get the default gpg pub key if available
    - Rather than add a fake web-flow user I've added this as an endpoint on /api/v1/signing-key.gpg
    - [x] Try to match the default key with a user on gitea - this is done at verification time
- [x] Make things configurable?
    - app.ini configuration done
    - [x] when checking commits are signed need to check if they're actually verifiable too
- [x] Add documentation

I have decided that adjusting the docker to create a default gpg key is not the correct thing to do and therefore have not implemented this.

* Change tests to make it possible to run TestGit with 1.7.2

* Make merge run on 1.7.2

* Fix tracking and staging branch name problem

* Ensure that git 1.7.2 works on tests

* ensure that there is no chance for conflicts

* Fix-up missing merge issues

* Final rm

* Ensure LFS filters run on the tests

* Do not sign commits from temp repo

* Restore tracking fetch change

* Apply suggestions from code review

* Update modules/repofiles/temp_repo.go

* Be more strict with git arguments
* fix-up commit test
* use bindings for branch name

No need to convert to the same type.

* Add options to git.Clone to make it more capable

* Begin the process of removing the local copy and tidy up

* Remove Wiki LocalCopy Checkouts

* Remove the last LocalRepo helpers

* Remove WithTemporaryFile

* Enable push-hooks for these routes

* Ensure tests cope with hooks

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Remove Repository.LocalCopyPath()

* Move temporary repo to use the standard temporary path

* Fix the tests

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Remove LocalWikiPath

* Fix missing remove

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Use AppURL for Oauth user link (#6894)

* Use AppURL for Oauth user link

Fix #6843

* Update oauth.go

* Update oauth.go

* internal/ssh: ignore env command totally (#6825)

* ssh: ignore env command totally

* Remove commented code 

Needed fix described in issue #6889

* Escape the commit message on issues update and title in telegram hook (#6901)

* update sdk to latest (#6903)

* improve description of branch protection (fix #6886) (#6906)

The branch protection description text were not quite accurate.

* Fix logging documentation (#6904)

* ENABLE_MACARON_REDIRECT should be REDIRECT_MACARON_LOG

* Allow DISABLE_ROUTER_LOG to be set in the [log] section

* [skip ci] Updated translations via Crowdin

* Move sdk structs to modules/structs (#6905)

* move sdk structs to moduels/structs

* fix tests

* fix fmt

* fix swagger

* fix vendor

* Allow git.GetTree to take both commit and tree names, return full paths on entries listed through Tree.ListEntriesRecursive

Signed-off-by: Filip Navara <filip.navara@gmail.com>

* Fix the SHA returned on Git Tree APIs called with commit hash or symbolic name

Signed-off-by: Filip Navara <filip.navara@gmail.com>

* Use go-git for tree reading and commit info lookup.

Signed-off-by: Filip Navara <navara@emclient.com>

* Use TreeEntry.IsRegular() instead of ObjectType that was removed.

Signed-off-by: Filip Navara <navara@emclient.com>

* Use the treePath to optimize commit info search.

Signed-off-by: Filip Navara <navara@emclient.com>

* Extract the latest commit at treePath along with the other commits.

Signed-off-by: Filip Navara <navara@emclient.com>

* Fix listing commit info for a directory that was created in one commit and never modified after.

Signed-off-by: Filip Navara <navara@emclient.com>

* Avoid nearly all external 'git' invocations when doing directory listing (.editorconfig code path is still hit).

Signed-off-by: Filip Navara <navara@emclient.com>

* Use go-git for reading blobs.

Signed-off-by: Filip Navara <navara@emclient.com>

* Make SHA1 type alias for plumbing.Hash in go-git.

Signed-off-by: Filip Navara <navara@emclient.com>

* Make Signature type alias for object.Signature in go-git.

Signed-off-by: Filip Navara <navara@emclient.com>

* Fix GetCommitsInfo for repository with only one commit.

Signed-off-by: Filip Navara <navara@emclient.com>

* Fix PGP signature verification.

Signed-off-by: Filip Navara <navara@emclient.com>

* Fix issues with walking commit graph across merges.

Signed-off-by: Filip Navara <navara@emclient.com>

* Fix typo in condition.

Signed-off-by: Filip Navara <navara@emclient.com>

* Speed up loading branch list by keeping the repository reference (and thus all the loaded packfile indexes).

Signed-off-by: Filip Navara <navara@emclient.com>

* Fix lising submodules.

Signed-off-by: Filip Navara <navara@emclient.com>

* Fix build

Signed-off-by: Filip Navara <navara@emclient.com>

* Add back commit cache because of name-rev

Signed-off-by: Filip Navara <navara@emclient.com>

* Fix tests

Signed-off-by: Filip Navara <navara@emclient.com>

* Fix code style

* Fix spelling

* Address PR feedback

Signed-off-by: Filip Navara <navara@emclient.com>

* Update vendor module list

Signed-off-by: Filip Navara <navara@emclient.com>

* Fix getting trees by commit id

Signed-off-by: Filip Navara <navara@emclient.com>

* Fix remaining unit test failures

* Fix GetTreeBySHA

* Avoid running `git name-rev` if not necessary

Signed-off-by: Filip Navara <navara@emclient.com>

* Move Branch code to git module

* Clean up GPG signature verification and fix it for tagged commits

* Address PR feedback (import formatting, copyright headers)

* Make blob lookup by SHA working

* Update tests to use public API

* Allow getting content from any type of object through the blob interface

* Change test to actually expect the object content that is in the GIT repository

* Change one more test to actually expect the object content that is in the GIT repository

* Add comments

* move code.gitea.io/git to code.gitea.io/gitea/modules/git

* fix imports

* fix fmt

* fix misspell

* remove wrong tests data

* fix unit tests

* fix tests

* fix tests

* fix tests

* fix tests

* fix tests

* enable Debug to trace the failure tests

* fix tests

* fix tests

* fix tests

* fix tests

* fix tests

* comment commit count tests since git clone depth is 50

* fix tests

* update from code.gitea.io/git

* revert change to makefile

* Explicitly disable Git credential helper

If the user running Gitea has configured a credential helper, Git
credentials might leak out of Gitea.

There are two problems with credential helpers when combined with Gitea:

1. Credentials entered by a user when doing a migration or setting up a
   mirror will end up in the credential store. In the worst case, this
   is the plain text file ~/.git-credentials.
2. Credentials in the credential store will be used for migrations and
   mirrors by all users. For example, if user A sets up a mirror, their
   credentials will be stored. If user B later sets up a mirror from the
   same host and does not enter any credentials, user A's credentials
   will be used.

This PR prepends -c credential.helper= to all Git commands to clear the
list of helpers. This requires at least Git version 2.9, as previous
versions will try to load an empty helper instead. For more details, see
24321375cd

* Update git module

- Update import paths from github.com/go-gitea to code.gitea.io
- Fix import path for travis

See https://docs.travis-ci.com/user/languages/go#Go-Import-Path

* Replace gogits/git-module dependency with go-gitea/git

Fixes #92

* Remove git alias for git module import (not needed)