Add GPS duty cycling

[awolden]

• Adds configurable GPS duty cycling to EnviromentalSensorManager

[4np]

It would be nice if the polling interval could be variable, based on accelerometer values (for example 3-axis RAK1904 or 9-axis RAK12034).

If there's no accelerometer, default to 5 mins, and if there's an accelerometer and acceleration is detected then adjust the GPS update interval based on the acceleration rate.

[awolden]

@4np ya I considered adding some more sophistication to it, we could wait for a minimum accuracy, take an average over 3 readings, waiting for accelerometer values, I didn't want to try add too much too fast when some of this can be layered on. (plus I don't have an accelerometer to test with)

[4np]

Yeah makes sense, it probably deviates too far from the scope of the PR. Still something that would be nice to have on the roadmap at some point.

[fdlamotte]

As I've played a little with gps lately I think I'll handle this one ;) I think idea and implementation are good

@awolden have you considered implementing pwm in the LocationProvider instead of sensor manager ? I think it might make sense ...

For debugging, the new ui page I propose in #820 will be good, it shows sat count, fix status and coordinates as they come from nmea ...

I'll wait for #820 before going further, as it removes unnecessary duplicate code between sensor manager and location provider ;)

[awolden]

I can move it, will have time to do that soon