Support data plane RBAC for E2E tests. (#2176)

* Acquire token for NoSQL account prior to running tests.

* Change client id to user assigned managed identity.

* Change to use managed identity. Add token variables for gremlin and
tables.

* Add RBAC details to test README.

* Add token for SQL readonly database. Skip resource token tests when RBAC
enabled.

* Use hardcoded account name for sql readonly.

* Use specific tag for sql readonly.

* Remove comment.

src/Contracts/ViewModels.ts

@@ -443,6 +443,7 @@ export interface DataExplorerInputsFrame {
     [key: string]: string;
   };
   feedbackPolicies?: any;
+  aadToken?: string;
 }
 
 export interface SelfServeFrameInputs {