Currently loki `alertingRule` objects are rejected if the query  does not reference the namespace the alert is created in. 

The object is rejected with the following error: 

Error "Invalid value: "<query>":rule needs to have a matcher for the namespace" for field "spec.groups[0].rules[0].expr

We have a similar RFE in the metrics monitoring space requesting this much requested feature
https://issues.redhat.com/browse/OBSDA-237