util: Add reviewers using account ID's when possible

util: Add reviewers using account ID's when possible

Currently, there are some accounts that cannot be added as a
reviewer due to unknown conflicts associated with the email address.

This commit adds the ability for the bot to use
ReviewerInfo._account_id when possible, and to use email addresses
otherwise.

To reduce the number of queries to the server, a json file will be
created in .data/ to store known account ID's.

Change-Id: I9887bec12d14279e61119a615687a339e3f9c994
Signed-off-by: Hoa Nguyen <hoanguyen@ucdavis.edu>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/38236
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>