This PR cleans up the docs in a way to make them simpler to ingest by
our [docs repo](https://gitea.com/gitea/gitea-docusaurus).

1. It includes all of the sed invocations our ingestion did, removing
the need to do it at build time.
2. It replaces the shortcode variable replacement method with
`@variable@` style, simply for easier sed invocations when required.
3. It removes unused files and moves the docs up a level as cleanup.

---------

Signed-off-by: jolheiser <john.olheiser@gmail.com>

This was intended to be a small followup for
https://github.com/go-gitea/gitea/pull/23712, but...here we are.

1. Our docs currently use `slug` as the entire URL, which makes
refactoring tricky (see https://github.com/go-gitea/gitea/pull/23712).
Instead, this PR attempts to make future refactoring easier by using
slugs as an extension of the section. (Hugo terminology)
- What the above boils down to is this PR attempts to use directory
organization as URL management. e.g. `usage/comparison.en-us.md` ->
`en-us/usage/comparison/`, `usage/packages/overview.en-us.md` ->
`en-us/usage/packages/overview/`
- Technically we could even remove `slug`, as Hugo defaults to using
filename, however at least with this PR it means `slug` only needs to be
the name for the **current file** rather than an entire URL
2. This PR adds appropriate aliases (redirects) for pages, so anything
on the internet that links to our docs should hopefully not break.
3. A minor nit I've had for a while, renaming `seek-help` to `support`.
It's a minor thing, but `seek-help` has a strange connotation to it.
4. The commits are split such that you can review the first which is the
"actual" change, and the second is added redirects so that the first
doesn't break links elsewhere.

---------

Signed-off-by: jolheiser <john.olheiser@gmail.com>

As title.

- **Installation**: includes how to install Gitea and related other
tools, also includes upgrade Gitea
- **Administration**: includes how to configure Gitea, customize Gitea
and manage Gitea instance out of Gitea admin UI
- **Usage**: includes how to use Gitea's functionalities. A sub
documentation is about packages, in future we could also include CI/CD
and others.
- **Development**: includes how to integrate with Gitea's API, how to
develop new features within Gitea
- **Contributing**: includes how to contribute code to Gitea
repositories.

After this is merged, I think we can have a sub-documentation of `Usage`
part named `Actions` to describe how to use Gitea actions

---------

Co-authored-by: John Olheiser <john.olheiser@gmail.com>

Add `markdownlint` linter and fix issues. Config is based on the one
from electron's repo with a few rules relaxed.

This updates the log path in the [gitea-docker] jail configuration
to match the path in the [gitea] jail, which was updated in #13726.

Following the merging of #14959 - Gitea is a lot more strict regarding the interpretation of `X-Real-IP` and `X-Forwarded-For` headers.

This PR updates the fail2ban documentation to include hints to set: `REVERSE_PROXY_TRUSTED_PROXIES` and `REVERSE_PROXY_LIMIT` appropriately.

See discussion in #16443

Co-authored-by: zeripath <art27@cantab.net>

Following the merge of #16278 we need to update the fail2ban
documentation to take account of the availability of the new
sshConnectionFailed failed authentication attempt log message.

Also add a deprecation notice regarding the previous publicKeyHandler
messages, as these may be a source of false positives.

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

Continuing on from #13953 continue to improve and standardise
logging from internal SSH.

Also updates the fail2ban setup

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

Co-authored-by: 6543 <6543@obermui.de>
Co-authored-by: Lauris BH <lauris@nix.lv>

* Log IP on SSH authentication failure

fixes https://github.com/go-gitea/gitea/issues/13094

* include string 'Failed authentication attempt' in error

* update fail2ban docs

also match failed authentication over command line

* better logging of authentication errors with IP addresses

* format ...

Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: 6543 <6543@obermui.de>

* Changed path from /home/git/gitea/log/gitea.log to
  /var/lib/gitea/log/gitea.log on the fail2ban page, so the log matches
  the instructions found on the following binary installation page:
  https://docs.gitea.io/en-us/install-from-binary/#create-required-directory-structure

* Fix hugo shortcode typo in faq

* Switch to using language tags

Fix typo in doc fail2ban-setup.md