[LUA] Allow spawning donkeys as animals

[kubaau]

In S2 RTX scripts, !ADD_ANIMAL with an ID of 7 spawned donkeys as animals. This is mostly useless (and possibly annoying because the donkeys cannot be hunted and are immortal in S2) but it does see use in 2NDpaign chapter 1 and adds to the chaos which is created by design when launching the scenario (there are immediately fires and donkeys running around):

[Spikeone]

Well in a RttR implementation, I'd see them as homeless donkeys which die after a while (so they are not immortal). You can also create a a bit likewise effect, by placing another HQ close, adding only donkeys as resource and then forcing that player to surrender.

[kubaau]

Hmmmm... maybe a dummy donkey player with an HQ immediately being destroyed is not such a bad idea. It would indeed eliminate the need for this ticket and solve the "issue" that the donkeys are immortal (which gets really confusing) and would actually add to the confusion if a player is immediately defeated (which in this scenario is welcome).