Allow baby_monster to support monstergroups

[Karol1223]

Is your feature request related to a problem? Please describe.

I have been endlessly complaining about why vertebrates should not upgrade into mutants. I stand by this notion, but it would be nice to allow the mutant population to increase in older maps anyway. This could be achieved by giving a low chance for vertebrates with mutant variants to give birth to a mutant version of themselves instead of a normal baby.

This cannot be currently achieved, as baby_monster does not support monstergroups.

Solution you would like.

Support for monstergroups in baby_monster

Describe alternatives you have considered.

No response

Additional context

No response