Add command to invite authors to Triage all/provided dandisets

For overall integration with github for issues/questions tracking: https://github.com/dandi/dandi-archive/pull/1595/files

Command should allow for two modes of operation
- "sync": get a list of users already known/invited to the dandiset, get current list known to dandiset, add/invite users on github to ensure that lists are in sync
- "explicit": allow for explicit specification which user to add or remove (so could be used "smartly" as a reaction to edit of authors via metadata edition)

Users will need to be added in Triage role -- they must not have write permissions.

Command would later be interfaced also to be used/triggered by authorized users via the bot (#360)