Improvement: support action group and metric linking

[t3mi]

Describe the current behavior
With the introduction of MetricAlert and ActionGroup resources, its not possible to "link" them as-is (through the references or configmap etc.) and user need to manually concatenate various parts to get the full armId value of the action group which would be subsequently parsed in MetricAlert resource.

Describe the improvement
It would be helpful if MetricAlert could support reference to the ActionGroup in the same namespace in addition to the full armId.

[theunrepentantgeek]

Good suggestion. We'll look into doing this for the next release.

Leaving needs-triage so that we discuss this when we resume our weekly sync in the new year.

[matthchr]

To put specifics on this, the ActionGroupId should be labelled as an ARM ID.

That's from this bit of Swagger: https://github.com/Azure/azure-rest-api-specs/blob/main/specification/monitor/resource-manager/Microsoft.Insights/stable/2018-03-01/metricAlert_API.json#L470

[matthchr]

Could we make this fix in a nonbreaking way by overriding the JSON deserialize of the CrossResourceReference type?

[matthchr]

@theunrepentantgeek volunteered to see if we can fix this in a newer version.

[theunrepentantgeek]

Unfortunately, version 2018-03-01 is the most recent version of this particular resource, negating any possibility of using a version upgrade as an injection point for a silent upgrade.

Could we make this fix in a nonbreaking way by overriding the JSON deserialize of the CrossResourceReference type?

We should revisit this suggestion from @matthchr

[theunrepentantgeek]

Overriding deserialization of genruntime.KnownResource won't help because we also change the property name - ActionGroupId becomes ActionGroupReference.

We have a potential design to fix this issue in #4543.