Support "mute list" of servers to collect metrics from, but not generate alerts

[jkuester]

For some CHT servers (e.g. development instances) it is useful to track metrics, but is not necessary/desirable to generate alerts for the instance (or at least not in the same way as alerts are triggered for a production instance).

An MVP of this feature would just be a configurable list of "muted servers" that will not trigger any alerts (or even just not send any alert notifications).

Other solutions could include specific mute-lists for each alert rule or notification categories where a server could have a configurable "alert level"....