Incorrect document version

[wxiaoguang]

https://docs.gitea.com/usage/authentication#reverse-proxy

@lunny @techknowlogick

[lunny]

This is caused by the authentication have been moved to https://docs.gitea.com/administration/authentication in v1.23. In theory, the old documentation should be removed but not.

[wxiaoguang]

Actually only a few documents need to be really "versioned".

Most page could simply share the same version, no need to duplicate the documents a lot for different versions.

At the moment, only "config options" is the only page which really need to be versioned, see #17879