code-owners plugins wants a git ref in Gerrit (e.g. refs/heads/master)
while Depot Tools wants a local git ref (e.g. refs/remotes/origin/main,
or a git hash).

Add an upstream parameters to be used by Depot Tools, separate from
a Gerrit ref expected by owners_client.

Change-Id: Ieed97a186e3140b3f82830efa189dbe3e4d8c806
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2730049
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>