Feature Request: support reference commands which allow for multiple lables

[Hugo-Heagren]

Some referencing commands (like \cref) allow taking a single argument, but with multiple, comma-separated labels. I use these occasionally and they're really handy when they're appropriate.

Since consult-reftex-insert-reference uses consult-read which (along with consult--multi) can only return a single candidate, I could see it being implemented as a separate command (e.g. consult-reftex-insert-multi-references) with consult-completing-read-multiple. This doesn't allow for categories (see minad/consult#468), but that might not be so bad, since quite often multi-label refs are are used to refer to things of many types (e.g. 'Eqs. 6-9 and figs. 1-5').

[karthink]

I'll take a crack at this soon.