reqwest-retry: does it support the Retry-After header?

[bbigras]

Does it support Retry-After?

The Retry-After response HTTP header indicates how long the user agent should wait before making a follow-up request. There are three main cases this header is used:

When sent with a [503](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/503) (Service Unavailable) response, this indicates how long the service is expected to be unavailable.
When sent with a [429](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/429) (Too Many Requests) response, this indicates how long to wait before making a new request.
When sent with a redirect response, such as [301](https://developer.mozilla.org/en-US/docs/Web/HTTP/Status/301) (Moved Permanently), this indicates the minimum time that the user agent is asked to wait before issuing the redirected request.