Easy to design. I would go for an OPAMP to do a voltage comparisation with a reference voltage and a simple flipflop circuit as start/stop. Controling a relay and some resistors wits some switches to select the discharge rate.

My home build 2S discharger is basically doing the same but using a LiPo alarm as low voltage detection.
https://www.rctech.net/forum/radio-e...ischarger.html