Correct usage of Characteristic.VolumeSelector and Characteristic.VolumeControlType?
### Current Situation

I am struggling to understand how to use `Characteristic.VolumeSelector` and `Characteristic.VolumeControlType`. Is there any documentation or an example of how to use these correctly?

What I am looking for is a way to step-wise increment/decrement a speaker's volume _without_ having to get the current volume first (just like pressing a VOL+ button on a physical remote).

From my tests, it appears that `Characteristic.Volume` always expects the _absolute_ value as a number regardless of any other specified characteristic. Hence, I thought I'd have to use `VolumeControlType.RELATIVE` and `VolumeSelector` to implement step-wise control:

```TYPESCRIPT
this.service = this.accessory.getService(this.platform.Service.TelevisionSpeaker) || this.accessory.addService(this.platform.Service.TelevisionSpeaker);

//...

this.service.setCharacteristic(this.platform.Characteristic.VolumeControlType, this.platform.Characteristic.VolumeControlType.RELATIVE_WITH_CURRENT);
this.service.getCharacteristic(this.platform.Characteristic.VolumeSelector)
  .onSet((value)=>{
    this.platform.log.debug('Set Characteristic Volume via VolumeSelector ->', value);
    if (value === this.platform.Characteristic.VolumeSelector.INCREMENT) {
      this.exampleStates.Volume += 1; //increment
    } else {
      this.exampleStates.Volume -= 1; //decrement
    }
  });
````
However, this does not appear to be working. While the characteristics are visible in Homebridge's Web-UI when clicking on the little gear icon, there is no way to set the `VolumeSelector`. In Eve, I can set it, but only to `0` and `1`!

Have I misunderstood the concept and am doing something wrong here? Or am I using everything correctly and the stuff is simply not supported by any of the UIs?

### Logs

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### Configuration

```json
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```


### Environment

n/a

### Process Supervisor

hb-service

### Additional Context

_No response_