@retry should respect 429 `Retry-After` headers

[prkumar]

Discussed in #235

^{Originally posted by mivade December 20, 2021}
RFC 6585 describes the 429 status code to indicate hitting rate limits. This type of response may include a Retry-After header indicating the time in seconds to wait before trying again. Naively I would expect to be able to define my own backoff function to parse this header and yield that value to indicate how long to wait, but it looks like backoff functions have no knowledge of the response itself. Is there a way to get this functionality?

[prkumar]

Some additional context: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Retry-After

[prkumar]

The new RetryBackoff class is available now in v0.9.6!