refs: add `committer_info` to `ref_transaction_add_update()`

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>