proto: Deprecate fine-grained repository maintenance RPCs

Historically we had and still have lots of fine-grained RPCs which perform repository maintenance in Gitaly. This meant that control of how repositories are packed does not reside in Gitaly though, and this is starting to become a bigger problem because we cannot easily iterate on how repositories should be maintained. We have thus recently extended the black-box-style maintenance RPC OptimizeRepository with the intent of making it the single source of truth for how repositories are packed.

Deprecate the old fine-grained repository maintenance RPCs. They will be removed as soon as all callers have been migrated to OptimizeRepository, which will then allow us to improve the general repository maintenance strategy.

Changelog: deprecated