Simple default retry policy for idempotent targets.
If your target is non-idempotent, use default_retry_non_idempotent instead.
Retries on 429 (Too Many Requests), 502 (Bad Gateway),
503 (Service unavailable), and 504 (Gateway Timeout), as well as on any
ConnectionError, ConnectionFailedError and TimeoutError.
Uses max_retries of 5, and backoff as per retry.default_backoff.
For more information, see Retry steps.