Unify issues search behavior by always filtering when ALL labels matches
As explained on #26315 (closed), this MR unifies the way we filter issues by labels by always returning issues that matches ALL given labels. This also leads to simpler and reusable code/behavior.
- Changelog entry added
- Documentation created/updated
- API support added
- Tests
- Added for this feature/bug
- All builds are passing
- Conform by the merge request performance guides
- Conform by the style guides
-
Branch has no merge conflicts with
master(if it does - rebase it please) - Squashed related commits together
Closes #26315 (closed) EE-backport gitlab-ee!1258