Support UAMI/Workload Identity for running self-hosted github runners on AKS

# Goal
I would like to use workload identity for authenticating towards Azure and my container registry. I am using workload identities for everything else.

# Context
We are using ARC (https://github.com/actions/actions-runner-controller) which is the officially endorsed Microsoft/Github way to run actions on K8S hardware. We are running on an AKS cluster with VMSS and the action still fails.

You state that it is supported on Azure VM's only (https://github.com/Azure/login/#login-with-user-assigned-managed-identity), but it doesn't seem to include scale sets?

Docker is using your action in their documentation, so it was a surprise to us that their solution didn't work: https://github.com/docker/login-action#openid-connect-oidc

This seems to be somewhat of an oversight, ARC is an old project and it seems strange that the official Azure action wouldn't support it.

# Similar issues
https://github.com/Azure/login/issues/293