[Feature Request] Add support and documentation for using raw adminLists without hitting slack

[Jack Ellenberger]

Now that I have abdicated my throne at Braintree, my subjects are still passing me adminLists with the latest emoji, but I don't have access to the slack instance itself. Methods like sync should be able to take an adminlist instead of an authjson and just use that. A few things to note:

1. isn't that just an emojme-upload? yes it is, but whatever. document it
2. can't you already do it without auth if you poke the file to make it look fresh to emojme, then specify garb as the token and cookie? yes, but that ux does not spark joy.

This is more a documentation and testing problem than a code problem, but it's a requested feature none the less.