We should offer the ability to redirect abuse reports to a room.

This issue has been migrated from [#11148](https://github.com/matrix-org/synapse/issues/11148).

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The current Admin API to fetch abuse reports is not really convenient.

This gives homeserver administrators two possibilities:

1. Write a script to fetch abuse reports from the admin API and publish it somewhere readable, typically a room. It's possible but annoying to implement and deploy.
2. Configure a reverse proxy to intercept calls to `/report` and publish them somewhere readable, typically a room. Mjölnir recently started offering this feature but it's still a pain to configure correctly and extends the security perimeter of homeservers that use the feature.

We should consider the following change:

- publish abuse reports directly to a room, as structured messages (possibly based on [MSC3215](https://github.com/matrix-org/matrix-doc/pull/3215));
- let the admin pick a user id, room id, etc. in homeserver.yaml to determine which user will publish these reports and where;
- encourage admins to adopt a bot to turn these structured messages into human-readable, internationalized, abuse reports.

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- log to room