add optional escalation policy to aws account and cluster

[maorfr]

with an escalation policy referenced from an aws account or a cluster, we can use dynamically generated per-resource alerts that will alert the tenant instead of AppSRE.

[patjlm]

Don't we have escalation policy from namespace->app already? Which scenario would require account/cluster link without namespace?

[maorfr]

the scenario is someone looking for a cluster owner (that is not us) and not for a service owner.

[geoberle]

i like this a lot, again a nice option to reduce alerts on us and hand them to the owners of clusters and accounts

[rporres]

I see the scenario of defining a cluster/account owner and I like the idea. I honestly don't see how this can be used to route catch-all alerts to tenants since that involve being able to associate alerts labels to apps (which is something I've been wanting to do for a while, but other stuff keeps coming).