Compatibility with PostgreSQL 15 beta1 (#2299)

* update postgresql/validator.py
* pg_rewind doesn't like if there are unix sockets in PGDATA
* pg_rewind now supports --config-file option

postgres1.yml

@@ -113,7 +113,7 @@ postgresql:
     # Fully qualified kerberos ticket file for the running user
     # same as KRB5CCNAME used by the GSS
 #    krb_server_keyfile: /var/spool/keytabs/postgres
-    unix_socket_directories: '.'
+    unix_socket_directories: '..'  # parent directory of data_dir
   basebackup:
       - verbose
       - max-rate: 100M