How do you use http to trigger doorbell button? Nothing in the Wiki/Readme
**Describe The Problem:**
The description states:
`doorbell: Exposes the doorbell device for this camera. This can be triggered with the dummy switches, MQTT messages, or via HTTP, depending on what features are enabled in the config. (Default: false)`

I would like to use a http command to activate the doorbell trigger button, but I see no instructions on how to do so


**Homebridge Config:**

```json
    {
                    "name": "Front Door FFMPEG",
                    "manufacturer": "xxxx",
                    "model": "xxxx",
                    "serialNumber": "1234",
                    "firmwareRevision": "1.0",
                    "motion": true,
                    "motionTimeout": 1,
                    "doorbell": true,
                    "doorbellSwitch": true,
                    "switches": true,
                    "videoConfig": {
                        "source": "-re -ignore_loop 0 -i file:///home/pi/Public/fuo.gif",
                        "maxStreams": 2,
                        "maxWidth": 1280,
                        "maxHeight": 720,
                        "maxFPS": 10,
                        "maxBitrate": 300,
                        "vcodec": "libx264",
                        "audio": false,
                        "packetSize": 1316,
                        "vflip": false,
                        "hflip": false,
                        "debug": false
                    }
                }
```


**Environment:**

* **Node.js Version**: <!-- node -v -->  v12.18.3
* **NPM Version**: <!-- npm -v --> v6.14.7
* **Homebridge Version**: <!-- homebridge -V --> 1.2.0-beta.31
* **Homebridge Camera FFmpeg Version**:  homebridge-camera-ffmpeg v2.4.2
* **Homebridge Config UI X Plugin Version**: homebridge-config-ui-x v4.24.0
* **Operating System**: <!-- Raspbian / Ubuntu / Debian / Windows / macOS / Docker --> Raspbian GNU/Linux Buster (10)


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