Attaches a custom domain to an application by its ID.
example.com). Use "@" to remove the custom domain.success if successful, error if not.error if not successful.UNAUTHORIZED: The user is not authenticated or lacks sufficient permissions.PLAN_RESTRICTED_FEATURE: The user’s plan does not support custom domains.INVALID_CUSTOM_DOMAIN: No custom domain was provided.INVALID_CUSTOM_DOMAIN_FORMAT: The provided domain format is invalid.FORBIDDEN_DOMAIN: The provided domain is restricted.DOMAIN_ALREADY_IN_USE: The provided domain is already in use by another application.APP_NOT_FOUND: The specified application does not exist or does not belong to the user.USER_LIMITS_NOT_FOUND: The user’s plan limits could not be found.NO_CONFIG_FILE: The application’s configuration file is missing.INVALID_CONFIG: The application’s configuration file is invalid.INVALID_MEMORY: The requested memory is invalid or exceeds plan limits.FAILED_TO_REBUILD_APP: The application could not be rebuilt with the new configuration.