Allow u_add_trait to specify a variant

[MNG-cataclysm]

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

I've been trying to make some stuff, and I noticed that the u_add_trait dialogue effect cannot specify a variant, at least according to the documentation. This would be really helpful for EOC related things, so I think that it'd be nice to have.

Solution you would like.

Allow u_add_trait to specify a variant, kind of like this:

"effect": { "u_add_trait": "test_trait", "variant": "blue" }

Describe alternatives you have considered.

None.

Additional context

None at this time.