scylla_rsyslog_setup adds a configuration file to rsyslog to forward the
trances to a remote server.
It will override any existing file, so it is safe to run it multiple
times.
It takes an ip, or ip and port from the users for that configuration, if
no port is provided, the default port of Scylla-Monitoring promtail is
used.
Signed-off-by: Amnon Heiman <amnon@scylladb.com>