Update Puppet Server docs for jruby-settings 'profiling-mode'

After some research it turns out that this profiling option does not enable profiling all of the puppet-server jruby code. Instead, it only profiles the single thread that starts the puppet-server service and none of the child threads. After a quick hipchat discussion with puppet server team we decided for now we should just update the docs, and create SERVER-2253 to explore options with that setting in the future.

https://puppet.com/docs/puppetserver/5.3/config_file_puppetserver.html

The descriptions for this option should be updated to something like:

profiling-mode: Optional. Used to enable JRuby’s profiler for service startup and set it to one of the supported modes. The default value is off, but it can be set to one of api, flat, graph, html, json, off, and service. See ruby-prof for details on what the various modes do.