Make /Position writeable on the service
Make /Position writeable on the service

/Position was not writeable, hence it was not possible to chane the position
by writing to the service (like you can with the Role). Make this possible so it
can be adjusted just like the role.

victronenergy/dbus-cgwacs,victronenergy/dbus-cgwacs,victronenergy/dbus-cgwacs