Select collections to push / export

[WilhelmKrohmer]

Hey! I think it would be very handy to be able to select, if I want to generate one JSON for all collections or individual collections as individual JSONs. For example I am structuring component-level tokens per collection and export them for my developers individually (button.token.json, card.token.json, etc.), so that we have tidy JSONs. If I would be able to select which collections I want to export and if they should be in one or multiple JSONs, I would have much more control over the file structure and be able to fit it to my needs.