Remove misleading haproxy enabled flag

General MR

Summary

The "enabled" toggle for HAProxy has never actually done anything, and only serves to confuse customers. This MR removes it and adds a comment that explains when it is actually enabled.

Closes https://repo1.dso.mil/platform-one/big-bang/bigbang/-/issues/181

Closes https://repo1.dso.mil/platform-one/big-bang/bigbang/-/issues/279