Allow external metrics requests to be done with different multiple identities

[elutsky]

What we are trying to achieve:

We have different namespaces (teams), accessing external (azure resources) metrics.
We would like those teams each to use it's own Azure AAD Identity - to ensure least privilege access.
At the best scenario, we would even like to access each resource with separate Identity ,(AAD Pod Identity project).

We are fine with both installing single shared Keda metrics server, Wich will pick the identities from CRD per resource or something like that, or having KEDA metrics server installed per namespace.

We just looking the external requests for the metrics to be done at least by per-namespace identities.

If you think it is impossible with current Keda architecture - can you explain which workaround can be taken, and to provide some draft of estimation for this effort - we'd consider the contribution here.