Support PostgreSQL Databases

[carsonab]

Adds support for PostgreSQL:

• PostgreSQL database connections with TLS
  • Local testing can be done against a alloydbomni container
  • Added gencerts.sh to create certs used in local server config and client tests to enable TLS tests
• AlloyDB connections using alloybd-go-connector
• Uses single database driver pgx

Local testing can be done against a alloydbomni container, which uses the same database engine as hosted AlloyDB, using a normal postgres connection. Connections with a alloydb-go-connector need a GCP AlloyDB instance to connect to. However both connection methods use the same database driver. This means our local testing of business logic and its sql queries use the same database driver and engine as higher environments, and only the connection method will differ between environments.

Tested with alloybd-go-connector successfully using hosted AlloyDB instance for both IAM and native db login.

TODOs:

• handle closing dialer from alloydbconn.NewDialer
• fix CI runners (these tests pass locally on macOS with docker desktop)

NOTE:

• Tested client certs by manually editing the server's pg_hba.conf to require client certs with hostssl all all all scram-sha-256 clientcert=verify-full but not automated to do that

[adamdecaf]

Is there a reason we format a DSN here but for vanilla postgres use their URI syntax?

[carsonab]

Either should work. I just preferred the key=value syntax when not giving a server (since thats handled by the alloydbconn library when connecting to a hosted AlloyDB instance)