Some bots use git-cl to upload changes to Gerrit.
Add an option so those can set Bot-Commit+1 on upload
instead of TBR and CR+1.

Change-Id: I5e80ddadedf6c4fe277f8984c35a603da923de5e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2679780
Commit-Queue: Josip Sokcevic <sokcevic@google.com>
Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Auto-Submit: Edward Lesmes <ehmaldonado@chromium.org>