Now roll_merge_gerrit.py waits for a +1, and immediately submits. With
auto-submit and rubber-stamper bot, this makes the script fully
fire-and-forget.

This also fixes the commit message update to include the change id.

Bug: v8:12849
Change-Id: I63784bfc1b2a16dfcd308b11e67d9da9c2ff3f8a
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3804249Reviewed-by: Liviu Rau <liviurau@google.com>
Commit-Queue: Liviu Rau <liviurau@google.com>
Auto-Submit: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/main@{#82664}