Electrolyzer state: adding stanby mode

[Alematiale]

At present electrolyzer can only work in ON or OFF state.
Consider adding STANDBY mode where electrolyzer does not produce any hydrogen but consumes the power needed to maintain the system temperature and pressure so that it can rapidly resume production when renewable electricity is available.
Values to be considered: 1-5% of the electrolyzer full load capacity.
Ref: https://arxiv.org/abs/2301.05310