Allow for alternative monitoring solutions

[arthurdm]

Currently the monitoring key in our CRD is specific to Prometheus' ServiceMonitor. As k8s / OKD / OpenShift is used in many different cloud environments there are some popular solutions we may be asked to support.

One of them is IBM Cloud App Management (ICAM). There are others from other vendors.

So this issue suggests a change to our CRD, to allow for extensions to be added to our operator over time, increasing its out-of-the-box value add.

For example:

monitoring:
   prometheus:
     ....

monitoring:
   icam:
     ....

We should investigate if there's a way our operator can be backwards compatible with current CRs, so if one of the known types is not found under monitor we default to the current behaviour which is Prometheus.