Do not treat columns with partial unique indexes as unique in psql driver

[adsa95]

This PR fixes a bug in the psql driver where partial unique indexes will mark a column as unique, which is not true as it is only unique over a subset of rows. This currently leads to bugs such as #1436 where incorrect relations are generated (one-to-one instead of one-to-many) but could potentially also lead to other bugs where this difference is important.

This fix is implemented by adding a condition to the query in *PostgresDriver.loadUniqueColumns that excludes partial indexes by filtering on the pg_index.indpred column which will be null if it is not a partial index as stated in the PostgreSQL docs:

indpred pg_node_tree
Expression tree (in nodeToString() representation) for partial index predicate. Null if not a partial index.

[stephenafamo]

Add a note in CHANGELOG.md 🙏🏾

[adsa95]

@stephenafamo done! Also reverted some accidental autoformatting that was not meant to be included.