[BUILDBOT] Add facilities to manipulate tokens

Summary:
This will be used to give the user a discrete immediate feedback when
calling the bot from comments. Since this is persistent it could also be
used to build an anti DoS mechanism.

Depends on D8085.

Test Plan:

pytest

Reviewers: #bitcoin_abc, deadalnix

Reviewed By: #bitcoin_abc, deadalnix

Differential Revision: https://reviews.bitcoinabc.org/D8086