[1.0.0] Various optimizations (PDO list, cn=monitor)

[ChadSikorra]

Just a few various fixes as I do more load testing to see where things start to break down at scale (>25k entries, multiple clients hammering the server in parallel).

1. Add a default limit based on the look-through limit if one is not already set. This helps prevent pulling more entries then we would ever actually go through in different situations.
2. Batch metrics rollups for cn=monitor. Without batch, and under load, this causes back-pressure that's quite bad. Only realized this when I went to enable cn=monitor in the load test to get real server side stats so the numbers don't only show the client side of the story.
3. Enabling cn=monitor by default in load tests. Adding more options to the load test in general.