Function send_notice 

async fn send_notice(
    services: &Services,
    target: &UserId,
    event_type: Option<&str>,
    state_key: Option<&str>,
    content: Raw<RoomMessageEventContent>,
) -> Result<OwnedEventId>

Sends an event from the server identity into the target’s notice room.

Reuses prior rooms and invites recipients who are neither joined nor invited. Membership and notice events are appended under the same room lock.