This PR adds a section to the documentation that links to the project
[Opengist](https://github.com/thomiceli/opengist) on GitHub.
The feature was proposed in #16670 but didn't resonate well with the
maintainers.
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.
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Signed-off-by: jolheiser <[email protected]>
crapStone
Marcin Kuźmiński
John Olheiser