Ability for publishers to shadowban users from their groups

A partner publisher has encountered users who repeatedly post unwanted annotations in a publicly readable group that belongs to them. They want to hide these users' posts from others without too visibly alerting the offending users (ie. they want to shadowban / NIPSA these users).

We currently provide the ability to moderate individual annotations but this only allows for post-publication moderation.

We have a couple of implementation options here:

- This partner is using third party accounts so we could expose the existing NIPSA functionality to them via an API and let them shadowban that user everywhere.
- In future it seems likely that publishers using first-party accounts will probably want similar capabilities for groups that they maintain, so another option might be to give publishers the ability to shadowban users within a specific context (ie. groups they have admin rights over).