Add "`max_results_per_request" to /meta endpoint

[dmarx]

I think the default used to be 500 and got bumped up to 1000. Had to hardcode this into PSAW's defaults. Would be nice if we could reuse the pattern we created for rate-limiting, i.e. have the PSAW instance ask the API for the current state of its limitations. This also would make it seamless to expand limits if you give special access based on user perms or something like that in the future.