Refactor debezium demo towards a perf oriented version.

[jcferretti]

The load generation script also listens on a local port for a command line interface where we can control the rates of purchases and pageviews:

cfs@erke 13:00:12 ~/dh/oss3/deephaven-core
$ docker exec -it core-debezium-demo_loadgen_1 /bin/bash -c "echo set purchases_per_second 13 | nc -N localhost 8090"
LOADGEN Connected.
Setting purchases_per_second: old value was 10, new value is 13.

Lots of improvements in logging to be able to more closely track what the loadgen script is doing.