Sprinkler Controller to Support Both a Main Valve and a Pump

**Describe the problem you have/What new integration you would like**
In the Sprinkler Controller, I would like to specify both a main valve and a pump. Currently can specify one pump_switch_id (or pump_on_switch_id/pump_off_switch_id), which controls a pump or a main valve. I would like to specify both a pump and a main valve.

**Please describe your use case for this integration and alternatives you've tried:**
My irrigation system is feed from a rain barrel, so it has a main valve and a pump (because of low pressure from the barrel). Downstream are zone valves. Both the main value and the pump must be turned on. The main valve is a latching valve, the pump is simple on/off. Main valve and pump are controlled through different GPIO. Using the Sprinkler Controller, I see no direct way to turn on both the latching main valve, and the pump, when turning on the zones.

I've though about using a template switch for the pump_switch_id (not sure if it will work), but would prefer it natively in the Sprinkler Controller.

**Additional context**

Start with the Sprinkler Controller entry point and review how pump_switch_id, pump_on_switch_id, and pump_off_switch_id currently control a pump or main valve. Check whether a template switch can cover the described setup, then define how separate GPIO-controlled latching main-valve and simple on/off pump controls should activate with the zones. Done means both devices can be specified and operated together.

Written by the indexing model from the issue text.