Add Programming Tab support for vtx pit mode

[MartinHugh]

Currently it is possible to use the Programming tab to control vtx Power, Band and Channel.

It would be really useful to add the ability to set vtx Pit Mode as well, so that this can be set (for example) from a transmitter switch.

[MartinHugh]

I note that for HDZero (which is my use case) this functionality is possible by setting the VTX power to max index +1, which configures 0mW. It is possible to switch from 0mW through the power levels using the programming tab,

I am not sure if there is any demand for this feature on system other than HDZero, but since it works for that system using the above workaround, I am happy for this issue to be closed.