Transmitter health flag for FAA MOC

Document F3586-22 (attached) requires checking if Transmitter radio hardware and software are functioning properly.
That's in chapters: 7.2.3.2 and 7.3.2.2 that are further referenced in tests in chapter 8 (8.8.2 and 8.9.6).

I see in the code that there are no checks that transmitter is working properly.
There is a flag `pfst_check_ok` but it doesnt have any effect as its just set to `true`.
The radio has to be tested pre flight, but also in flight, as the mentioned chapters of F3586-22 require.

Is there a way of checking whether the transmitter is working properly? Is there a plan of implementing this feature?

[F3586-22 Standard Practice for Remote ID Means of Compliance (1).pdf](https://github.com/ArduPilot/ArduRemoteID/files/11041508/F3586-22.Standard.Practice.for.Remote.ID.Means.of.Compliance.1.pdf)

Start by locating where `pfst_check_ok` is set and consumed, and determine why setting it to `true` has no effect. Compare the existing behavior with F3586-22 chapters 7.2.3.2, 7.3.2.2, 8.8.2, and 8.9.6. Done means transmitter radio hardware and software health are checked both pre-flight and in flight.

Written by the indexing model from the issue text.