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.
Since we already have a key/cert combination in /etc/puppedb/ssl you should be able to use those and save the trouble of copying. I think looking at the source sslcertfile and sslkeyfile are the options one can inject just like you've done here with sslrootcert.

In the JKS method though, it required the CN of the certificate to match the user you were connecting as. In this case the CN would be the hostname of the machine. Hopefully it doesn't work this way with LibPQ, just something to watch out for.