feat(catalog): add placeholder for identity API implementation

packages/storybook/.storybook/apis.js

@@ -11,6 +11,8 @@ import {
   ErrorAlerter,
   GoogleAuth,
   GithubAuth,
+  identityApiRef,
+  MockIdentity,
 } from '@backstage/core';
 
 const builder = ApiRegistry.builder();
@@ -19,6 +21,8 @@ const alertApi = builder.add(alertApiRef, new AlertApiForwarder());
 
 builder.add(errorApiRef, new ErrorAlerter(alertApi, new ErrorApiForwarder()));
 
+builder.add(identityApiRef, new MockIdentity());
+
 const oauthRequestApi = builder.add(
   oauthRequestApiRef,
   new OAuthRequestManager(),