Support multiple datasets in a single file

(Regarding additional changes to support cli use for USDM validation, #631) There is one item I don't quite agree with:
> - The ".json" at the end is needed so that the correct data reader is used.

It seems wrong to pretend that a single json file is multiple json files at the Engine level. I think it would be better to fix the engine to be able to handle different types of dataframe collections (folder of files, single file, cosmos collection of items, etc). But this might be a much bigger change, in which case the hack is okay for now and you can create a new ticket for it instead.

_Originally posted by @gerrycampion in https://github.com/cdisc-org/cdisc-rules-engine/pull/631#pullrequestreview-1977457315_