Throttle should slow submission down rather than return error

Currently, if you exceed the throttling limit, the client returns a `MaxRequestsExceeded` error. In my opinion the client should throttle submissions to the allowed limit under-the-hood.

No files or tests are named in the issue. Start by locating the client throttling logic and references to MaxRequestsExceeded, then trace how submissions are sent and where the limit is enforced. Done means submissions are delayed to stay within the allowed limit instead of returning that error.

Written by the indexing model from the issue text.