Handle cardinality limits on the server side

Problem/Motivation

#2566871: Better handle cardinality added some limits on the front-end side of the story. We need to handle cardinality on server side too.

Proposed resolution

We need to be able to tell entity browser how many items we need from it. We need to figure out how we'll be sending that information and possibly do it in a way that will allow us to send arbitrary limits in the future.