Fixes #39046

Fixes gitaly#629

Replaces all the explicit include metadata syntax in the specs (tag:
true) into the implicit one (:tag).
Added a cop to prevent future errors and handle autocorrection.

If the ref doesn't exist, and the source branch is deleted, we can't get it back
easily. Previously, we ignored this error by shelling out, so replicate that
behaviour.

This allows the current Gitaly migration to depend on less code outside
of the Gitlab::Git module

Users of project mirrors would see that the number of branches did not
match the number in the branch dropdown because remote branches were
counted when Rugged was in use. With Gitaly, only local branches
are counted.

Closes #36934

Also fix a few tests

so that we don't have to fetch it for non-forks

Signed-off-by: Rémy Coutable <remy@rymai.me>

This helps keep the abstraction layers simpler, and also keep the
interface of those methods consistent, in case of implementation
changes.

Closes gitaly#415

Closes gitaly#355