`/logout` does not take a request body, which is inconsistent

Other PUT and POST requests except for media upload take a JSON request body, even if that's just `{}`.

For some reason `/logout` is an exception to this, although it's not clear why or whether this is just an accident.

Area: https://spec.matrix.org/v1.8/client-server-api/#post_matrixclientv3logout

Read the linked Matrix Client-Server API section for POST /_matrix/client/v3/logout and compare its request-body definition with the other PUT and POST endpoints. Confirm the intended consistency rule and update the specification so the logout endpoint's request-body behavior is explicit; done means the section clearly resolves whether an empty JSON body is required or allowed.

Written by the indexing model from the issue text.