disable prometheus adapter when monitoring_enabled is false

From: https://cern.service-now.com/nav_to.do?uri=incident.do?sysparm_query=number=INC3365942%26sysparm_view=it_operations_management

Not sure we want to add this. When we where installing with magnum the validation that monitoring_enabled was true was happening when installing the prometheus-adapter but not when we moved to helm.

There is a label for prometheus_adapter_enabled so maybe this is not usefull.