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:

![grafik](8f132760-882c-4ab8-9678-77e47dfc4415)

modules/util/slice.go

@@ -4,6 +4,7 @@
 package util
 
 import (
+	"cmp"
 	"slices"
 	"strings"
 )
@@ -45,3 +46,10 @@ func SliceSortedEqual[T comparable](s1, s2 []T) bool {
 func SliceRemoveAll[T comparable](slice []T, target T) []T {
 	return slices.DeleteFunc(slice, func(t T) bool { return t == target })
 }
+
+// Sorted returns the sorted slice
+// Note: The parameter is sorted inline.
+func Sorted[S ~[]E, E cmp.Ordered](values S) S {
+	slices.Sort(values)
+	return values
+}