refs: add committer_info to ref_transaction_add_update()

The `ref_transaction_add_update()` creates the `ref_update` struct. To
facilitate addition of reflogs in the next commit, the function needs to
accommodate setting the `committer_info` field in the struct. So modify
the function to also take `committer_info` as an argument and set it
accordingly.

Signed-off-by: Karthik Nayak <karthik.188@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

refs/refs-internal.h

@@ -162,6 +162,7 @@ struct ref_update *ref_transaction_add_update(
 		const struct object_id *new_oid,
 		const struct object_id *old_oid,
 		const char *new_target, const char *old_target,
+		const char *committer_info,
 		const char *msg);
 
 /*