Serverless function UI (#6388)

https://www.figma.com/design/xt8O9mFeLl46C5InWwoMrN/Twenty?node-id=36235-120877

Did not do the file manager part. A Function is defined using one unique
file at the moment

Feature protected by featureFlag `IS_FUNCTION_SETTINGS_ENABLED`

## Demo


https://github.com/user-attachments/assets/0acb8291-47b4-4521-a6fa-a88b9198609b

packages/twenty-server/src/engine/metadata-modules/serverless-function/utils/serverless-function-graphql-api-exception-handler.utils.ts

@@ -17,6 +17,7 @@ export const serverlessFunctionGraphQLApiExceptionHandler = (error: any) => {
       case ServerlessFunctionExceptionCode.SERVERLESS_FUNCTION_ALREADY_EXIST:
         throw new ConflictError(error.message);
       case ServerlessFunctionExceptionCode.SERVERLESS_FUNCTION_NOT_READY:
+      case ServerlessFunctionExceptionCode.FEATURE_FLAG_INVALID:
         throw new ForbiddenError(error.message);
       default:
         throw new InternalServerError(error.message);