Alerts from MCO are missing namespace

Description of problem:
Current prometheus rules for MCO do not define namespace:
https://github.com/openshift/machine-config-operator/blob/master/install/0000_90_machine-config-operator_01_prometheus-rules.yaml#L98

As per style guide namespace should be included: https://github.com/openshift/enhancements/blob/master/enhancements/monitoring/alerting-consistency.md#style-guide

Version-Release number of selected component (if applicable):

4.11.x but most likely older versions impacted too.

How reproducible:

always

Steps to Reproduce:

1. Trigger any alert from MCO (i.e. allocate a lot of memory on control plane)

Actual results:

Alert has no namespace indicating source

Expected results:

Most likely "openshift-machine-config-operator" namespace label is defined for the alerts.

I suppose this is a 4.12+ change if anything.