Feature: allow to specify VIP in watchdog_setup.

Feature: allow to specify VIP in watchdog_setup.

This commit allows to specify VIP parameter (delegate_ip) in
watchdog_setup using new option "-vip [ip]". If ip is omitted,
'127.0.0.1' is assumed. Even if vip option is specified, pgpool will
not actually set the VIP to the system: if_up_cmd, if_down_cmd are
just set to echo command and do nothing except emit a log. This option
is intended to trace the action of Pgpool-II regarding VIP handling.

Author: Tatsuo Ishii <ishii@postgresql.org>
Discussion: https://www.postgresql.org/message-id/20250820.151646.1640218512808280876.ishii%40postgresql.org