[Feature Request] Expose speakers volume as dimmable light switch

[Marcel-Lambacher]

Feature Request

Goal

I would like to be able to control the volume of Sonos speakers within my HomeKit app.

Implementation

Speakers that are discovered by homebridge-sonos-multiroom should be exposed as dimmable light switches. Changing the "virtual" light will change the volume for a specific device.

Further notes

If this is a feature that isn't already planned yet, I would like to implement it myself and provide a PR.

[lukasroegner]

I think this is a great extension that absolutely makes sense. I would gladly accept your PR!