[grundfosalpha] Add support for Grundfos Alpha3

[jlaur]

As discussed in #15907 extending support for Grundfos Alpha3 seems doable. See #15907 (comment).

This issue is created to keep track of resources, discussions and progress towards implementing this support.

Other projects having an implementation:

• https://github.com/esphome/esphome/tree/dev/esphome/components/alpha3

[jlaur]

I tried taking a few baby steps, but so far completely without success. In a new handler I added some logging:

    @Override
    public void onScanRecordReceived(BluetoothScanNotification scanNotification) {
        super.onScanRecordReceived(scanNotification);
        byte[] manufacturerData = scanNotification.getManufacturerData();
        logger.trace("onScanRecordReceived manufacturer data length: {}", manufacturerData.length);
        byte[] data = scanNotification.getData();
        logger.trace("onScanRecordReceived data length: {}", data.length);
    }

I get only empty byte arrays. Same when deriving from ConnectedBluetoothHandler rather than BeaconBluetoothHandler. It seems Alpha3 is a bit different than the Alpha Reader and requires more logic to be implemented.

FYI @tisoft

[tisoft]

Yea, alpha3 needs a real pairing connection. I will have a look, but I'm currently busy with other things.