[2/n]: Rest API -> TwentyORM migration POST rest/* (#9986)

# This PR

- Addressing #3644 
- Migrates the `POST rest/*` endpoint to use TwentyORM directly
- Adds integration tests
- Refactors common login in the v2 service file
- Refactors test utility files

packages/twenty-server/src/engine/core-modules/exception-handler/http-exception-handler.service.ts

@@ -51,7 +51,7 @@ export class HttpExceptionHandlerService {
 
     return response.status(statusCode).send({
       statusCode,
-      error: exception.code || 'Bad Request',
+      error: exception.name || 'Bad Request',
       messages: [exception?.message],
     });
   };