Consider adding averages

[kenchris]

https://www.kernel.org/doc/html/latest/accounting/psi.html makes the point that if you poll slower than 1 second, it makes more sense to look at averages over a time period (say 10s, 1m, 5m) as yo might be looking at a temporary spike.

This also makes sense as we express the sample-rate in hertz. We should in that case make throw when value is less than 1hz and limit the values to what the system supports.

We could expose the averages as part of PressureRecord and rename state to current and then add average10 etc. current could be undefined if samplerate was not set.

dictionary {
  PressureSource source;
  PressureState? current;
  PressureState average10;
  PressureState average60;
  PressureState average300;
  sequence<PressureFactor> contributingFactors;
  DOMHighResTimeStamp time;
};