Make the number of messages processed at a time by journal clients configurable
This setting needs to be tuned differently for different topics, as the size of objects varies quite wildly. Bumping the default to 200 reduces chatter in the consumer group which should reduce the amount of bandwidth used for consumption.
Depends on !129 (closed)
Test Plan
new test added to verify use of the batch_size parameter
Migrated from D2808 (view on Phabricator)