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.
I agree it should probably be _verify-full_. :+1: There's no point in verifying the CA chain if the CA cert the client/agent has doesn't even match the hostname of the CA. If we're going to take the time to document security, might as well do it right. Let me test it on my local install to ensure it works with _verify-full_ and then update the pull req.