Java: make a separate threat model kind for reverse DNS sources

[owen-mc]

I'm new to threat models, so I may be missing something that is required. In particular, is it okay to have a threat model kind that isn't part of the hierarchy controlled by this file?

Also, I searched for other reverse DNS sources and only found this one in C#, which seems to be only be used in one query currently. Any opinion on whether that should be made a source that applies to all queries and added to this new threat model kind? (I think this should be follow-up work.)