Add support for ScramSha256Plus

[vmihailenco]

Fixes https://github.com/go-pg/pg/issues/1483

[Neustradamus]

@vmihailenco: Good job!

SCRAM-SHA-256 has been added in PostgreSQL 10 SCRAM-SHA-256-PLUS variant (with TLS Binding) has been added in PostgreSQL 13 SCRAM-SHA-256 is selected by default in PostgreSQL 14

Links:

• https://www.postgresql.org/about/news/postgresql-10-released-1786/
• https://www.postgresql.org/about/news/postgresql-13-released-2077/
• https://www.postgresql.org/about/news/postgresql-14-released-2318/
• https://techcommunity.microsoft.com/t5/azure-database-for-postgresql/how-to-securely-authenticate-with-scram-in-postgres-13/ba-p/1548319