Update puppetDB docs to include info on LibPQFactory

Prior to this commit, the docs only enabled ssl for postgresql
connections. This commit changes the docs to add a few extra lines in
the database.ini file to use host cert/key and CA cert for verification
with ssl.
You need to be careful here. I presume we're not just doing SSL for a tick in the box, so I'd opt for verify-full to ensure the CN matches the hostname you are connecting to. An attack vector like this would require a cert, and the ability to get in the way of your request (like dns injection or arp poisoning) but with verify-full they have to have gotten the databases specific cert, with verify-ca they had to have only gotten a hold of any boxes certificate (and remember puppet runs everywhere, so every box has a signed cert). Basically verify-full will increases protection from dns injection and arp poisoning style attacks, and other network spoofing based attacks.

Your call, just warning you :-). We do "verify-full style" verification for most other services today I believe. At least this is generally true for agent->master->puppetdb.