Force stop an engine

Stops the engine immediately, skipping the graceful shutdown: the engine is torn down right away without closing its playlists first, so viewers may see playback fail instead of the stream ending cleanly. Works from any non-stopped state, including while the engine is stopping after a regular stop. The engine reports stopping until the teardown has completed (usually a few seconds), then stopped, and can only be started again once it is stopped. Prefer POST /engines/{id}/stop unless the engine has to be gone immediately. Returns 409 already_stopped for a stopped engine.