In the previous commit https://crrev.com/c/2532835 the option
to order branches by date was added. This CL adds a git config
variable cl.date-order than can be set to achive the same effect.

Change-Id: Iaf24c46c5f7b63b1e518c18aedc455808a2dc752
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2992887Reviewed-by: Josip Sokcevic <sokcevic@google.com>
Commit-Queue: Sigurd Schneider <sigurds@chromium.org>