Allow configuration of metrics server in mgmt-api

[burmanm]

What is missing?
Once the new /metrics work is done, we need the ability to allow easy configuration of filtering, ports and other properties of the /metrics server. This needs to be injected to the correct place in the deployment.

Either we extend the configuration of the operator to allow setting these (like ImageConfig) or we add a ConfigMap that's mapped (if it exists).

Why do we need it?

Environment

• Cass Operator version:

  Insert image tag or Git SHA here

Anything else we need to know?: