Extend UserAssignedIdentity operatorSpec with secrets

[mehighlow]

Describe the current behavior
UserAssignedIdentity can expose clientId, tenantId, and principalId in the form of a ConfigMap.

Describe the improvement
UserAssignedIdentity can expose clientId, tenantId, and principalId in the form of Secrets alongside ConfigMap.

Additional context
Some types of installations may require the secretKeyRef method for delivering Managed Identity credentials to the pod, either by design or for security reasons. Azure Service Operator (ASO) already supports exposing ConfigMaps and Secrets for a variety of resources. This functionality would extend to UserAssignedIdentity.