Do we need Metrics Scope in Scylla?

[wonderflow]

I think metrics scope is something like health scope. A metrics scope will aggregate metrics(such as CPU, Memory, QPS, etc) for multiple components in a configuration.

With a metrics scope, autoscaler can custom metrics for auto scale without caring about the detail.

Other traits, such as monitoring, alerting, can also use metrics scope along with health scope to trigger some actions.

Even health scope can use metrics scope to define whether it's healthy or not.

/cc @resouer @technosophos