plugin XEP-0359: use same ID as <message> for `origin_id`: even if the XEP doesn't specify if Message ID must be the same as `origin_id`, using a different one makes little sense, and is leading to bugs in other implementation (e.g. Movim using the wrong ID for reactions).

these certificates are used for demo purpose only. Those must be the same as in
backend_e2e (they are generated there)