OCPBUGS-8993: add namespace label to InstallPlanStepAppliedWithWarnings

The alerting consistency guide [1] requires the following:

`Alerts SHOULD include a namespace label indicating the alert's source.`

This change updates the expression of InstallPlanStepAppliedWithWarnings
to aggregate the result by namespace.

[1] https://github.com/openshift/enhancements/blob/master/enhancements/monitoring/alerting-consistency.md

Signed-off-by: Simon Pasquier <[email protected]>

Author: simonpasquier

Diff for: deploy/chart/templates/0000_90_olm_01-prometheus-rule.yaml

@@ -34,7 +34,7 @@ spec:
   - name: olm.installplan.rules
     rules:
     - alert: InstallPlanStepAppliedWithWarnings
-      expr: sum(increase(installplan_warnings_total[5m])) > 0
+      expr: sum by(namespace) (increase(installplan_warnings_total[5m])) > 0
       labels:
         severity: warning
       annotations: