Adds new Git auth configuration logic which sets up a global config
which applies to all repos for a Gerrit host, as well as a local
config if the current repo has a different user set up (e.g., someone
with multiple emails used across different repos for the same Gerrit
host).
Bug: b/351071334
Change-Id: I3a73a50b7ecc80ba22442de808b7f20a488ffc6f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/5723271
Reviewed-by: Yiwei Zhang <yiwzhang@google.com>
Commit-Queue: Allen Li <ayatane@chromium.org>