Add radio bandwidth display

[steveatinfincia]

A few weeks ago I added radio bandwidth stats to the old OSD as a diagnostic tool for people having latency issues, because the older layout only allowed users to see video bitrate.

However the radio bandwidth details are not part of the older telemetry stream, so the radio bandwidth data was added using shared memory and that only works on the pi itself.

And the OpenHD telemetry (sometimes referred to as simply "rssi") is sent as a packed C struct, which can't be changed without breaking a lot of things.

However we have a microservice channel now, and we have messages for it to carry that same telemetry data, so we can add the radio bandwidth data as an additional message without breaking anything.