Use BackstageUserIdentity, fix tests

Co-authored-by: blam <ben@blam.sh>
Co-authored-by: Fredrik Adelöw <freben@gmail.com>
Co-authored-by: Patrik Oldsberg <poldsberg@gmail.com>
Signed-off-by: Johan Haals <johan.haals@gmail.com>

plugins/techdocs/src/client.test.ts

@@ -44,6 +44,9 @@ describe('TechDocsStorageClient', () => {
     getProfile: jest.fn(),
     getUserId: jest.fn(),
     signOut: jest.fn(),
+    getProfileInfo: jest.fn(),
+    getBackstageIdentity: jest.fn(),
+    getCredentials: jest.fn(),
   };
 
   beforeEach(() => {