Document socket keep-alive options

With the explicit client ping removed (or disabled in older versions), there may be very little traffic on a given connection which may cause load balancers to timeout a connection in the middle of a long-running query. We should add docs to workaround this by setting the os level socket idle time: http://coryklein.com/tcp/2015/11/25/custom-configuration-of-tcp-socket-keep-alive-timeouts.html

With java 11 there are also java level socket configuration for setting that on a per socket basis that we can consider exposing.