Increase batch size to 10k documents

Summary:
I'm seeing a lot of getmores happening for our common pages since we
tend to do smaller numbers of bigger queries. The default batch size is
just 101 documents and a lot of our queries return more than that. From
some local benchmarking, I get a 10-20% speedup by setting batch size to
something large and just waiting for the whole resultset in one shot vs
doing it over a few queries.

Will see what impact this has in prod when it goes out, but shouldn't be
bad... just not clear how good it'll be.

Test Plan: Benchmarked both versions of the code

Reviewers: josh, jack, david

Maniphest Tasks: T6587

Differential Revision: http://infra1.corp.contextlogic.com/D10752