Read Response header for exact backoff time

[estherDow]

Hi Team,
I was looking into the way retries after a 429 Response are handled:
#48

to my understanding, this does not take the retryAfter response field into account, but exponentially increases backOff time.
https://www.dropbox.com/developers/documentation/http/documentation

https://developers.dropbox.com/dbx-performance-guide

If your application is uploading singular files as users interact with them, encountering this will be uncommon. The exception returns a Retry-After of zero, indicating that your application should simply retry the upload.

Would you be interested in a pr taking the retry after field into account?