[BUG] Initalize Git for hook regeneration

- Backport of #2416
- The hook regeneration code relies on `git.SupportProcReceive` being
set to determine if the `proc-receive` hook should be written, this
variable is set when the git module is initialized.
- Resolves #2414

(cherry picked from commit 815abad84c)

cmd/admin.go

@@ -428,6 +428,12 @@ func runRegenerateHooks(_ *cli.Context) error {
 	if err := initDB(ctx); err != nil {
 		return err
 	}
+
+	// Detection of ProcReceive support relies on Git module being initialized.
+	if err := git.InitFull(ctx); err != nil {
+		return err
+	}
+
 	return repo_service.SyncRepositoryHooks(graceful.GetManager().ShutdownContext())
 }