Merge #143664

143664: sql/cmd/roachtest: improve pg_regress RLS test compatibility r=spilchen a=spilchen

Modify the rowsecurity.sql test from pg_regress to cover additional cases. This test makes heavy use of SET SESSION AUTHORIZATION, which CRDB doesn't support, so it has been adjusted accordingly. Additionally, the test relies on a user-defined function f_leak; modifications were made to allow this function to be created and used within the test.

Some incompatibilities remain. For example, CRDB doesn't support COPY FROM in the same way as Postgres, which affects the expected output of certain queries. Nevertheless, these changes improve the test suite.

Closes #137122

Epic: CRDB-11724
Release note: none

Co-authored-by: Matt Spilchen <[email protected]>

Author: craig[bot]