Extend SendAndRetryRequest to allow retry options (backoff and
ErrorFunc) to be passed in. Add a surface to the generated code
for storage to allow the manual layer to choose whether the request
is retried.

I tested this out via the manual layer by verifying that the
ObjectsInsertCall only retries now when WithRetry() is applied.

I still need to update the generator to ensure that the changes in
the generated file will persist and probably add some tests as well.
Thought I'd try and get an initial review first.