Admin API: Moderate / hide post pending manual review

[Crashdoom]

Pitch

To allow third-party apps to help combat spam, it would be useful to add a way to mark posts as "pending review" through an administrative API. Marking a post as "pending review" should prevent any pending notifications to the recipients, and create a report under the system instance account.

To the end-user, a post "pending review" would be indicated similar to user-level filtered posts, e.g. "Hidden: This message has been flagged for moderator review." A user should still be able to expand this post if they so choose.

My intended use-case for this would be to monitor the public streaming feed to identify content exhibiting known abusive behaviors, flag them as requiring review, and have our moderation team be able to take preemptive action prior to users being affected.

This should operate similarly to the anti-spam models used by most mailing lists which require that the list moderators approve potentially spam posts before they become visible to the other users of the mailing list.

Motivation

Currently, a lot of instances are facing waves of spam that are becoming problematic and overwhelming to deal with. However, as posts cannot be recovered once deleted it is currently risky to employ any use of automated tools to identify spam without taking an irrevocable action, or using reports and leaving the content active which results in repeated notifications from the spam.

Allowing automated tooling to effectively hide a post without removing it allows quick actions to be taken to prevent spam directly affecting end users, while preserving content that may be accidentally misidentified.