PostgreSQL: allow connection parameters to be specified (#7579)

As documented in
https://www.postgresql.org/docs/current/libpq-connect.html#LIBPQ-PARAMKEYWORDS

Multiple parameters are separated by a space.

tests/query_runner/test_pg.py

@@ -1,6 +1,16 @@
 from unittest import TestCase
 
-from redash.query_runner.pg import build_schema
+from redash.query_runner.pg import _parse_dsn, build_schema
+
+
+class TestParameters(TestCase):
+    def test_parse_dsn(self):
+        configuration = {"dsn": "application_name=redash connect_timeout=5"}
+        self.assertDictEqual(_parse_dsn(configuration), {"application_name": "redash", "connect_timeout": "5"})
+
+    def test_parse_dsn_not_permitted(self):
+        configuration = {"dsn": "password=xyz"}
+        self.assertRaises(ValueError, _parse_dsn, configuration)
 
 
 class TestBuildSchema(TestCase):