Add Postgres as dependency in Praefect

Based on #1495 (closed), we decided postgres is the right place to persist state of nodes and replication jobs.

The first step to using postgres is to include it as a dependency. The goal of this issue is to

add a config field to specify the address of postgres
initiate a database connection when praefect starts up and write a log showing the connection was successful

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information