Postgres destination version detection inconsistent with best practices and tap-postgres #835

What sparked this was attempting to connect Crate DB as a destination which failed.

The crate staff the responded with this:
https://community.crate.io/t/stitch-data-cannot-connect-detecting-cratedb-version-instead-of-postgres-version/1273/2

This a technicality in the implementation but would align expected behaviour across the broader ecosystem.