Log schema when connecting to system database (#673)

This logs the custom engine URL and also the schema when connecting to
the system database, which helps ensure you know what you are connected
to.

I used f-string formatting, since that was the convention in the
repository. However, wanted to note that in general using %-formatting
with parameters (e.g. `log("%s", var)`) does have less performance
impact if the log level isn't hit due to the avoided string
interpolation.

---------

Co-authored-by: Peter Kraft <petereliaskraft@gmail.com>