As part of gitlab-org/gitaly#884, this commit contains the client
implementation for both TagNamesContaintingCommit and
BranchNamesContainingCommit. The interface in the Repository model stays
the same, but the implementation on the serverside, e.g. Gitaly, uses
`for-each-ref`, as opposed to `branch` or `tag` which both aren't
plumbing command. The result stays the same.

On the serverside, we have the opportunity to limit the number of names
to return. However, this is not supported on the front end yet. My
proposal to use this ability: gitlab-org/gitlab-ce#42581. For now, this
ability is not used as that would change more behaviours on a feature
flag which might lead to unexpected changes on page refresh for example.