Revisit `cortex get` output in relation to grafana

[vishalbollu]

cortex get performs the following operations:

• display a summary of API metrics
• make metrics available programmatically (important for batch)

cortex get is tightly coupled with prometheus. If prometheus goes down, the user currently has no way of getting any API state. In addition some of the metrics in cortex get are better consumed via grafana.

Come up with a design that displays the status of the APIs with as few dependencies on prometheus as possible and makes it easy for users to consume metrics in the intended way (either by grafana or programmatically).