`POST /_matrix/client/v3/rooms/{roomId}/forget` fails to define a request body

**Link to problem area**: https://spec.matrix.org/v1.16/client-server-api/#post_matrixclientv3roomsroomidforget

**Issue**

Presumably the client has to provide an empty JSON object as a body, given the [API standards](https://spec.matrix.org/v1.16/client-server-api/#api-standards)? But that should be clarified in the definition of the API.

Start with the linked Matrix Client-Server API section for POST /_matrix/client/v3/rooms/{roomId}/forget and compare it with the API standards linked in the issue. Clarify whether the request requires an empty JSON object, so the endpoint definition unambiguously describes the request body.

Written by the indexing model from the issue text.