This ensures the right caches are flushed when adding a branch via the
UI, instead of only flushing this one random cache.

This ensures Repository#add_tag calls Repository#before_push_tag instead
of just 1 random cache expiration method.

This ensures that Repository#rm_branch calls
before_remove_branch/after_remove_branch instead of just 1 random cache
expiration method.

The methods used for this are Repository#tag_count and
Repository#branch_count which cache their output in Redis as well as
memoizing it in an instance variable. Both methods have a corresponding
methods/hooks to flush the caches at the right time.

This is only needed when calling the "expire_cache" method as the other
expiration methods don't depend on Git data.