fix(core): Set up OAuth2 cred test (#6960)

https://linear.app/n8n/issue/PAY-728

packages/cli/src/constants.ts

@@ -45,6 +45,8 @@ export const RESPONSE_ERROR_MESSAGES = {
 	PACKAGE_LOADING_FAILED: 'The specified package could not be loaded',
 	DISK_IS_FULL: 'There appears to be insufficient disk space',
 	USERS_QUOTA_REACHED: 'Maximum number of users reached',
+	OAUTH2_CREDENTIAL_TEST_SUCCEEDED: 'Connection Successful!',
+	OAUTH2_CREDENTIAL_TEST_FAILED: 'This OAuth2 credential was not connected to an account.',
 };
 
 export const AUTH_COOKIE_NAME = 'n8n-auth';