Support SET SESSION AUTHORIZATION in Postgres

[watford-ep]

Working through more Postgres compat and found that npgsql issues the following SQL when recycling a connection in a pool:

SET SESSION AUTHORIZATION DEFAULT;
RESET ALL;
CLOSE ALL;
UNLISTEN *;
SELECT pg_advisory_unlock_all();
DISCARD SEQUENCES;
DISCARD TEMP;

With #2078 the last piece of that puzzle is SET SESSION AUTHORIZATION.