Add 'PauseBoth' to override options

[mpartington]

As previously described in #686 , pausing the batteries completely at a SoC <20% is sometimes necessary to allow the OCV corrections to accurately run on the GivEnergy systems (firmware dependant). Since I raised the previous case to request Predbat automate this, the slot override functions have been added. This means it's now quite easy to set the batteries to discharge to an appropriate SoC and follow with a pause period. However there is not currently an option for them to go completely idle, for example if FreezeCharge (AKA PauseDischarge) is chosen (during a night time off peak slot), the battery will still charge at the 'leakage rate' of 0.1C, which is too high for the OCV (I tried this at the weekend).

Describe the solution you'd like There is a third pause option, not currently implemented that pauses both charge and discharge, with the selection "PauseBoth". Could this be implemented as an additional slot override function please?

Describe alternatives you've considered I would need an external automation to put Predbat into read only mode at the point I need the pause, then set system to PauseBoth and then turn read only off once complete.

Additional context OCV logic is described in #686