Request: Add abilit to change probe offset with M851 Z-<Offset>

[DatenThielt]

Not sure if its just me but I often have to change my Z-Offset to deal with different filament (Since the prusaslicer does not have a per filament height level)

I believe having this with the BLTouch Plugin fits hand in hand and should be fast to implement

The only oddities I have seen with this is that there is some random offset applied in either +1 or -1

Thanks for the great plugin!