Add support for multiple USB grabbers

[rice1204]

Feature request

What problem does this feature solve?

Supporting multiple USB grabbers can solve situations where a matrix is not viable for multiple devices (Shield, PS4/5, xbox, soundbars). This could potentially be a killer feature because there are a range of complexities in finding a matrix that can support a diverse range of modern features such as VRR, Dolby Vision, CEC, etc.

This support adds ability to avoid matrix splitters altogether and simply use a single splitter for each device.

There is also an economic benefit because the cost to purchase 2x or 3x splitters+grabber is similar or even less than purchasing a good matrix (based on current market conditions).

If the ability to switch via IP-based triggers (i.e. JSON API) existed, this also means physical remote controls for matrixes can be eliminated.

What does the proposed API look like?

Controls for selecting a specific USB grabber should ideally be accessible via UI and JSON API.

How should this be implemented in your opinion?

Similar to the current functionality for multiple LED instances, there could be the ability to turn on/off or select multiple grabber instances.

Are you willing to work on this yourself?

Yes, but I'm afraid I'm not familiar with coding. Happy to contribute in any way that I can