[hdpowerview] Support refresh of signal strength

[jlaur]

Channel signalStrength was added by #11198 while #11933 refactored the REFRESH command for shades to be relative to channel for requested item. The missing piece now is the signalStrength channel which currently cannot be refreshed on request.

As with #11260 I don't think it adds much value to add a job for automatically refreshing signal strength. However, the information is notoriously unreliable, so it would add value to be able to manually request an update (e.g. from a rule). Also it would make the REFRESH action feature complete as each channel would have a dedicated method assigned for requesting a hard refresh.

The PowerView app has a feature for explicitly requesting signal strength hard refresh:

I have captured the communication. Sending this request for a specific shade, here as concrete example for shade with id 36321:

GET /api/shades/36321?survey=true

Yields a response like this:

{
    "shade_id": 36321,
    "survey": [
        {
            "neighbor_id": 17805,
            "rssi": -84
        }
    ]
}

If it succeeds. If it fails, which also is quite likely to happen, just:

{}