Support liveness and readiness checks and expose them in a metrics server

[bcotton]

Deployment tools wants a health check, or it will complain.

Provide a default Operator implementation that checks for the status of known resources e.g. ApiServer, and hooks to add additional checks for other dependencies.

The config should also be included in any deployment tooling.

[radiohead]

I'm working on this already in the scope of a different issue – expect to see some updates in the coming week(s).