feat(pgdriver): Implement database/sql/driver.SessionResetter

[htdvisser]

This pull request implements the SessionResetter interface on pgdriver.Conn.

The SessionResetter can be useful to detect a closed or bad connection before we're trying to run queries on it. To make this work, we'd need some way to get the underlying net.Conn from *pgdriver.Conn, so I added a Conn() net.Conn method for that. This is similar to how *pgx.Conn lets you get the underlying *pgconn.PgConn.

[vmihailenco]

Thanks

[NirBarak-RecoLabs]

Just wanted to give a thumbs up - if I understand correctly this is the perfect solution for multi-tenancy. Since you already have an exclusive lock on the connection when the SessionResetter is called, you can apply row-level security on the connection immediately before the query is called.

Seems like an undervalued feature to me - it has great potential!