Action for temporary block homeserver users from sending messages to any room

This issue has been migrated from [#6014](https://github.com/matrix-org/synapse/issues/6014).

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At last time there are many problems with spammers on different Matrix homeservers. I searching ways to automate user spam sending detection on my homeserver and auto-block users, that send too much messages per time. Here https://github.com/matrix-org/synapse/issues/6007 is my feature request about statistics for detect spammers.

But automatic system will have false positives, so immediately deactivate login is too hard way for detected users, because deactivate action have no backward action? If I change password, user will can restore it via email or phone.

Better way is make problematic user read-only, and temporary block user for sending new messages to any room in specific time (eg next 24 hours).