Collect metrics on how much time Puppet Server spends sending and receiving data from PuppetDB

[npwalker]

https://docs.puppet.com/pe/2016.4/puppet_server_metrics.html#puppetdb-metrics

This should be as easy as adding these metrics to the additional_metrics param for puppet server. However, we also need to enable the metrics endpoint on puppetserver in versions prior to 2017.2 and I'm not sure if we can do that from here or if we have to just document a hiera key that allows turning it on.