TLS setup and tests were rather finicky. It seems that openssl 3
encrypts certificates differently than older openssl and it does it in
a way Go and/or pgx ssl handling code can't handle. It appears that
this related to the use of a deprecated client certificate encryption
system.
This caused CI to be stuck on Ubuntu 20.04 and recently caused the
contributing guide to fail to work on MacOS.
Remove openssl from the test setup and replace it with a Go program
that generates the certificates.
* Extract CONTRIBUTING.md
* Add instructions and scripts to setup standalone PostgreSQL server
that tests the various connection and authentication types.
