Unify simplistic dispatch logic between open-loop control and demand components

The code in h2integrate/control/control_strategies/demand_openloop_controller.py, h2integrate/control/control_strategies/converters/flexible_demand_openloop_controller.py, and h2integrate/control/control_strategies/openloop_controllers.py#L307 have very similar uses and could possibly be generalized to be a single method or function.

I think that combining them, and simplifying as appropriate, would be a valuable contribution to avoid maintaining very similar sets of logic implemented in very different ways in different places within the same package. I think the simplest implementation is h2integrate/control/control_strategies/demand_openloop_controller.py, which could maybe serve as the basis for a shared method.

It would likely be useful to still allow each component that uses the shared method or function to keep use-specific naming conventions rather than imposing potentially over-generalized names on users.