Add BGP route attack email notification service to metrics utilities / tools as descriptor endpoints are announced

Add a new opt-in/out? email notification service for relay operators for endpoints in descriptors as they are announced; before adding to consensus, as authorities may one day opt not to publish descriptors with endpoints under active attack.

As new descriptors are processed, sned an email alert to designated recipients if the listed endpoint is under an "active attack", as distinct from anomalous route changes or advertisement behavior, nor does it encompass benign incompetence affecting widespread route behavior of an indiscriminate nature.

Note that third parties may opt to receive email alerts of BGP attacks for arbitrary relay identities; this should be supported, and perhaps linked to via Atlas?

Rate limiting and or / summaries should be implemented to avoid sending excessive numbers of email notifications to the same recipient.

Trac:
Username: anon