Backport #28643

Fix #28247

Backport #28302 by @yp05327

Close #28287

## How to test it in local
convert Makefile L34 into:
```
cd .tmp/upstream-docs && git clean -f && git reset --hard && git fetch origin pull/28302/head:pr28302 && git switch pr28302
```

Co-authored-by: yp05327 <576951401@qq.com>

Backport #27500 by @silverwind

Duplicate headers in a single Markdown document are problemlematic
because the auto-generated links won't be stable. Enable this rule with
no exceptions which is also the default of `markdownlint`. For example:

```md
# A
## Example
# B
## Example
```
Docasaurus will generated `example` and `example-1` links for this. If
the first heading is altered, the link `example` will unexpectedly move
to the second example heading.

Ref: https://github.com/go-gitea/gitea/pull/27461#discussion_r1347987659

Co-authored-by: silverwind <me@silverwind.io>

Backport #27291 by @silverwind

Previously, the production build never output sourcemaps. Now we emit
one file for `index.js` because it is the most likely one where we need
to be able to better debug reported issues like
https://github.com/go-gitea/gitea/issues/27213. This will currently
increase the binary size of gitea by around 700kB which is what the
gzipped source map file has.

Also, I fixed the CSS sourcemap generation which was broken since the
introduction of lightningcss.

The chinese docs are machine-translated, please correct accordingly.

Co-authored-by: silverwind <me@silverwind.io>

Backport #27232 by @techknowlogick

update DB docs per feedback.
https://gitea.com/gitea/gitea-docusaurus/issues/69

Co-authored-by: techknowlogick <techknowlogick@gitea.com>

ref: https://gitea.com/gitea/homebrew-gitea/pulls/178

Service may fail to start at boot time with timeout
Resolves #26934

Co-authored-by: Nikolay Kobzarev <n.kobzarev@aeronavigator.ru>

fix
https://github.com/go-gitea/gitea/issues/25995#issuecomment-1674096710

---------

Co-authored-by: silverwind <me@silverwind.io>

Arch linux package link has changed from the community repo to the extra repo.
The link has been updated.

The setting `MAILER_TYPE` is deprecated.
According to the config cheat sheet, it should be `PROTOCOL`.

---------

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

Update part of the documents, translate English to Chinese.

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>