batch inserter: Limit payload sizes

Created by: efritz

We limit batch insertions of payloads by the number of rows inserted. We should also flush payload batches once they exceed a given threshold so that we don't overload the database.

This threshold should be controlled by environment variables on the services themselves, with some high maximum. This is meant to be adjusted by site-admins for instances with high database usage/resource ratios to reduce the size of each individual query.

Partially alleviates the issues described in #31738 (closed).