Downgrade PostgreSQL JDBC Driver to 42.7.3

[hhund]

Until pgjdbc/pgjdbc/issues/3365 is fixed and released, we need to downgrade org.postgresql:postgresql to 42.7.3.

Without the downgrade Binary resources can not be created if SQL statement debug logging is enabled.

The fix in 2.0.0 should be back-ported to 1.7.x.

[hhund]

Bug in postgresql JDBC driver has been fixed via the 42.7.6 release.
Dependency upgraded via PRs #321 (DSF 1.8.0) and #322 (DSF 2.0.0).