We should update the concept and procedure modules in  https://docs.openshift.com/container-platform/4.15/monitoring/managing-alerts.html#managing-core-platform-alerting-rules_managing-alerts to make it explicit that AlertingRule and AlertRelabelConfig objects must be created in the openshift-monitoring namespace when creating or modifying core platform alerting rules.

In the concept module, we say "Define and add new custom alerting rules by constructing a query expression based on core platform metrics in the openshift-monitoring namespace" already, and in the procedures for creating and modifying alerting rules say in step 1 to create the rule in openshift-monitoring namespace, and the sample code also has the same.

But we should clarify the wording in the overview section tp say that it's a requirement. We should also add an admonition saying it's required below step 1 of both procedures so that no one can have any doubt that it's a requirement.