Mute monitors with an annotation

[mjhuber]

Support for muting monitors by adding an annotation would be beneficial. For example, an annotation could be added to a kubernetes object:

kubernetes.io/astro/mute-until: "2019-12-30 00:00:00"

and a downtime would be created to turn off alerting for that object.

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[lucasreed]

One note: we shouldn't use kubernetes.io in the annotation name. astro.fairwinds.com is the prefix we use to override monitor fields. That should be appropriate here too.

[lucasreed]

I'll work on this.

[lucasreed]

Adding to v2 milestone to be built in from the beginning (if deemed necessary)