[metrics-alerts] Retiring metrics alerts in its current format

Hi everyone,

Moving forward we are going to use this list as a service only list where admins will be receiving information about metrics services. We are talking about heartbeats and logs. Because we don't want to spam subscribers with services internals we are going to unsubscribe most people from the list.

For discussions about metrics and activities from the Network health team you can subscribe to network-health@lists.torproject.org.

Cheers,

-hiro