Allow using adminAPI with built-in prometheus

In order to delete the data manually from Prometheus, an administrative HTTP API needs to be enabled (enableAdminAPI flag) within Prometheus custom resource.

Currently, this is only possible with the upstream prometheus-operator and not in Red Hat OpenShift Container Platform as cluster-monitoring-operator will override the change and hence this is currently not supported to modify Prometheus CR within openshift-monitoring namespace to use the `enableAdminAPI` flag.

For more information, check upstream documentation.