Add alert for ring members in non-active state

As an extension to #1960, we should consider adding an alert when ring members are in a non-active state for an unexpected amount of time.

I had suggested something like min by(cluster, namespace) (cortex_ring_members{name="distributor",state!="ACTIVE"}) > 0 for longer than 30min, but feedback from @pracucci highlighted:

• For some components not supporting the auto-forget feature (e.g. distributors till very recent times) it's expected to have non-ACTIVE ring members for a long time and everything works as expected anyway
• I think the query you're suggesting would suffer the false positives issue during rollouts