RFE: For the ability to set up persistent storage for Prometheus

**Introduction**
The customer would like the ability to set up persistent storage for Prometheus

**Issue**
Configuring Prometheus is not supported in ARO as shown in the Azure Red Hat OpenShift support policy.
Azure Red Hat OpenShift support policy [ https://learn.microsoft.com/en-us/azure/openshift/support-policies-v4#cluster-configuration-requirements ]

**Business impact on the customer**
- Can not predict reliable Capacity needs like PVC/Disk, CPU or memory.
- They update or replace the Nodes continuously. So they lose continuously metric history and are unable to use trend analysis.
- Unable after a simple pod restart of Prometheus to see anomalies inside our user workload and this disturbs incident handling.

**Request / Customers Expectations**
The customer would like to have persistent ARO cluster core metrics in the built-in Prometheus, so that I can calculate trends for at least over 60 days.
Acceptance crirteria:
- persistent also when pods are restarting
- out of the box with a standard retention time
- adjustable retention time