Fix some RPM registry flaws (#28782)
Related #26984
(https://github.com/go-gitea/gitea/pull/26984#issuecomment-1889588912)
Fix admin cleanup message.
Fix models `Get` not respecting default values.
Rebuild RPM repository files after cleanup.
Do not add RPM group to package version name.
Force stable sorting of Alpine/Debian/RPM repository data.
Fix missing deferred `Close`.
Add tests for multiple RPM groups.
Removed non-cached `ReplaceAllStringRegex`.
If there are multiple groups available, it's stated in the package
installation screen:
461d8b53c2