Integrating with External GraceDB Alert Dispatcher (EGAD) for improved alert performance

Alerts are now being handled externally with EGAD. In addition, alerts sent over Mattermost are now implemented and enabled by default.

Tasks:

• test container on gracedb-test
• fix test_phone.py and test_email.py unit tests
  • these were disabled due to switch to EGAD changing their behavior, fixing is maybe 30 minutes' work