Compatibility with PostgreSQL 14 (#1926)

PostgreSQL 14 changed the behavior of replicas when certain parameters (like for example `max_connections`) are changed (increased): https://github.com/postgres/postgres/commit/15251c0a.
Instead of immediately exiting Postgres 14 pauses replication and waits for actions from the operator.

Since the `pg_is_wal_replay_paused()` returning `True` is the only indicator of such a change, Patroni on the replica will call the `pg_wal_replay_resume()`, which would cause either continue replication or shutdown (like previously).

So far Patroni was never calling `pg_wal_replay_resume()` on its own, therefore, to remain backward compatible it will call it only for PostgreSQL 14+.

tests/test_postgresql.py

@@ -725,3 +725,8 @@ class TestPostgresql(BaseTestPostgresql):
     @patch.object(Postgresql, 'is_running', Mock(return_value=True))
     def test_set_enforce_hot_standby_feedback(self):
         self.p.set_enforce_hot_standby_feedback(True)
+
+    @patch.object(Postgresql, 'major_version', PropertyMock(return_value=140000))
+    @patch.object(Postgresql, '_cluster_info_state_get', Mock(return_value=True))
+    def test_handle_parameter_change(self):
+        self.p.handle_parameter_change()