Special handling of check_recovery_conf for v12+ (#2292)

When starting as a replica it may take some time before Postgres starts accepting new connections, but meanwhile, it could happen that the leader transitioned to a different member and the `primary_conninfo` must be updated.

On pre v12 Patroni regularly checks `recovery.conf` in order to check that recovery parameters match the expectation. Starting from v12 recovery parameters were converted to GUC's and Patroni gets current values from the `pg_settings` view. The last one creates a problem when it takes more than a minute for Postgres to start accepting new connections.

Since Patroni attempts to execute at least `pg_is_in_recovery()` every HA loop, and it is raising at exception, the `check_recovery_conf()` effectively wasn't reachable until recovery is finished, but it changed when #2082 was introduced.

As a result of #2082 we got the following behavior:
1. Up to v12 (not including) everything was working as expected
2. v12 and v13 - Patroni restarting Postgres after 1m of recovery
3. v14+ - the `check_recovery_conf()` is not executed because the `replay_paused()` method raising an exception.

In order to properly handle changes of recovery parameters or leader transitioned to a different node on v12+, we will rely on the cached values of recovery parameters until Postgres becomes ready to execute queries.

Close https://github.com/zalando/patroni/issues/2289

patroni/postgresql/__init__.py

@@ -387,7 +387,7 @@ class Postgresql(object):
         self._query('SELECT pg_catalog.pg_{0}_replay_resume()'.format(self.wal_name))
 
     def handle_parameter_change(self):
-        if self.major_version >= 140000 and self.replay_paused():
+        if self.major_version >= 140000 and not self.is_starting() and self.replay_paused():
             logger.info('Resuming paused WAL replay for PostgreSQL 14+')
             self.resume_wal_replay()