Move UpdaterWithHooks from git to hook package

UpdaterWithHooks wraps 'git update-ref' with executing the hooks by calling Gitaly's HookManager. While the Updater itself is just a plain 'update-ref' wrapper, UpdaterWithHooks ties more into Gitaly's domain types. This is prone to creating cyclic dependencies as anything that needs to use the 'update-ref' wrapper will also import the hook package from Gitaly. This creates a problem for TransactionManager as we are about to integrate some of the transaction logic in the hooks. Fix the cyclic dependency by moving UpdaterWithHooks into its own subpackage below the main 'hook' package.