edge cases for MetricConfiguration CRD

If enableAnnotations=false, then advanced metrics won't show up unless a MetricConfiguration CRD exists (metric modules are initialized via metricModule's Reconcile()). We should initialize with default context options instead.

Also, should we support MetricConfiguration CRD when enableAnnotations=true? Right now, we do not: https://github.com/microsoft/retina/blob/9248f0d140e5c93da77bdbdf5e43ea3b0029cfd4/controller/main.go#L254-L268