Fix#31002
1. Mention Make sure `Host` and `X-Fowarded-Proto` headers are correctly passed to Gitea
2. Clarify the basic requirements and move the "general configuration" to the top
3. Add a comment for the "container registry"
4. Use 1.21 behavior if the reverse proxy is not correctly configured
Co-authored-by: KN4CK3R <admin@oldschoolhack.me>
Follow #23290
Network error won't make content lost. And this is a much better
approach than "loading-button".
The UI is not perfect and there are still some TODOs, they can be done
in following PRs, not a must in this PR's scope.
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