[TC] [Cloud] Expose `MaxKeys` for `IterateObjects`

What's the issue?
For AWS, we used to limit the number of max keys that would be listed when checking if a prefix existed; this was slightly more efficient than the default page size of 1,000.

When we added the IterateObjects API, we lost that abstraction.

What's the fix?
All three cloud providers expose this option, we should add the ability to use it.