Add a new data service interface for getting source info for pallas call, not implemented yet, thus no-op.

PiperOrigin-RevId: 825979824

Author: zzzaries

frontend/app/services/data_service_v2/data_service_v2.ts

@@ -283,6 +283,12 @@ export class DataServiceV2 implements DataServiceV2Interface {
     }) as Observable<string|Blob|null>;
   }
 
+  // Not implemented.
+  getLloSourceInfo(sessionId: string, opName: string, host = ''):
+      Observable<string> {
+    return of('');
+  }
+
   getSearchParams(): URLSearchParams {
     return new URLSearchParams(
         window.sessionStorage.getItem('searchParams') || '',

frontend/app/services/data_service_v2/data_service_v2_interface.ts

@@ -85,6 +85,10 @@ export interface DataServiceV2Interface {
       programId?: string,
       ): Observable<string|Blob|null>;
 
+  // Pick first host in the list if not specified.
+  getLloSourceInfo(sessionId: string, opName: string, host?: string):
+      Observable<string>;
+
   getSearchParams(): URLSearchParams;
   setSearchParams(searchParams: URLSearchParams): void;