Move `public/*` to `public/assets/*`

Some old PRs (like #15219) introduced inconsistent directory system.

For example: why the local directory "public" is accessed by
`http://site/assets`? How to serve the ".well-known" files properly in
the public directory?

For convention rules, the "public" directory is widely used for the
website's root directory. It shouldn't be an exception for Gitea.

So, this PR makes the things consistent:

* `http://site/assets/foo` means `{CustomPath}/public/assets/foo`.
* `{CustomPath}/public/.well-known` and `{CustomPath}/public/robots.txt`
can be used in the future.

This PR is also a prerequisite for a clear solution for:
* #21942
* #25892 
* discourse.gitea.io: [.well-known path serving custom files behind
proxy?](https://discourse.gitea.io/t/well-known-path-serving-custom-files-behind-proxy/5445/1)

This PR is breaking for users who have custom "public" files (CSS/JS).
After getting approvals, I will update the documents.

----

## ⚠️ BREAKING ⚠️

If you have files in your "custom/public/" folder, please move them to
"custom/public/assets/".

---------

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

Fix #23409 

Developers could browse & preview the local SVG images files directly.

It still has clear output.

![image](https://user-images.githubusercontent.com/2114189/224317107-f4b26c76-e36a-4e80-9eee-d8dc2e16421f.png)


![image](https://user-images.githubusercontent.com/2114189/224317527-2d4ca131-978c-4933-b071-4bae483f06e1.png)

---------

Co-authored-by: silverwind <me@silverwind.io>
Co-authored-by: delvh <leon@kske.dev>

- Update all JS dependencies to latest version
- Disable two redundant eslint rules
- Adapt stylelint config to codebase
- Regenerate SVGs
- Make file editor spinner "reserve" height so page does not shift
- Tested katex, swagger, monaco

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>
Co-authored-by: 6543 <6543@obermui.de>

* Update JS dependencies

- Update all JS dependencies
- For octicons, rename trashcan to trash
- For svgo, migrate to v2 api, output seems to have slightly changed but icons look the same
- For stylelint, update config, fix custom property duplicates
- For monaco, drop legacy Edge support
- For eslint, enable new rules, fix new issues
- For less-loader, remove deprecated import syntax

* update svgo usage in generate-images and rebuild logo.svg with it

* Clean up SVG

* update per feedback

* fix css style

* Delete gitea.png

* no new line at end of file

* fix newline?

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

- Use original gitea logo on migrate page
- Add card styles and map colors to css vars
- Tweak migrate page, adding hover effect to cards

Co-authored-by: Lunny Xiao <xiaolunwen@gmail.com>

* first draft

* update gitea sdk to 9e280adb4d

* adapt feat of updated sdk

* releases now works

* break the Reactions loop

* use convertGiteaLabel

* fix endless loop because paggination is not supported there !!!

* rename gitea local uploader files

* pagination can bite you in the ass

* Version Checks

* lint

* docs

* rename gitea sdk import to miss future conficts

* go-swagger: dont scan the sdk structs

* make sure gitea can shutdown gracefully

* make GetPullRequests and GetIssues similar

* rm useles

* Add Test: started ...

* ... add tests ...

* Add tests and Fixing things

* Workaround missing SHA

* Adapt: Ensure that all migration requests are cancellable
(714ab71ddc)

* LINT: fix misspells in test set

* adapt ListMergeRequestAwardEmoji

* update sdk

* Return error when creating giteadownloader failed

* update sdk

* adapt new sdk

* adopt new features

* check version before err

* adapt: 'migrate service type switch page'

* optimize

* Fix DefaultBranch

* impruve

* handle subPath

* fix test

* Fix ReviewCommentPosition

* test GetReviews

* add DefaultBranch int test set

* rm unused

* Update SDK to v0.13.0

* addopt sdk changes

* found better link

* format template

* Update Docs

* Update Gitea SDK (v0.13.1)