Review handling of 429 errors

[daveplunkett]

I recently tightened the IP-Flood rule rate limit in our WAF. Now, requests from a single IP are limited to 2000 every 5 minutes. When you exceed this rate, you'll get a 429 error.

It would be great to handle this error gracefully and implement a backoff algorithm that allows the upload to succeed. This may already be working as desired! I can see 429s, but I don't know what happened at the customer end.

Thanks!