chore: convert dbauthz tests to also run with Postgres (#15862)

Another PR to address https://github.com/coder/coder/issues/15109.

- adds the DisableForeignKeysAndTriggers utility, which simplifies
converting tests from in-mem to postgres
- converts the dbauthz test suite to pass on both the in-mem db and
Postgres

coderd/database/queries/testadmin.sql

@@ -0,0 +1,20 @@
+-- name: DisableForeignKeysAndTriggers :exec
+-- Disable foreign keys and triggers for all tables.
+-- Deprecated: disable foreign keys was created to aid in migrating off
+-- of the test-only in-memory database. Do not use this in new code.
+DO $$
+DECLARE
+    table_record record;
+BEGIN
+    FOR table_record IN 
+        SELECT table_schema, table_name 
+        FROM information_schema.tables 
+        WHERE table_schema NOT IN ('pg_catalog', 'information_schema')
+        AND table_type = 'BASE TABLE'
+    LOOP
+        EXECUTE format('ALTER TABLE %I.%I DISABLE TRIGGER ALL', 
+                    table_record.table_schema, 
+                    table_record.table_name);
+    END LOOP;
+END;
+$$;