Separate system operations from core objects in GraphQL endpoints (#12977)

Moves system-level operations (auth, billing, admin) to use the
/metadata endpoint instead of /graphql.

This cleans up the endpoint separation so /graphql is purely for core
objects (Company, People, etc.) and /metadata handles all system
operations.

Part of prep work for webhook/API key core migration.

packages/twenty-front/src/testing/mockedApolloCoreClient.ts

@@ -0,0 +1,6 @@
+import { ApolloClient, InMemoryCache } from '@apollo/client';
+
+export const mockedApolloCoreClient = new ApolloClient({
+  uri: process.env.REACT_APP_SERVER_BASE_URL + '/graphql',
+  cache: new InMemoryCache(),
+});