Trouble with sending json Body
**Describe the bug**
I am having trouble sending a body in my URL request. I may be doing it wrong and perhaps this is just a request for better documentation. 

**Expected behavior**
I want to send JSON with my URL 

**To Reproduce**
Steps to reproduce the behavior:
1. Use the following configuratoin.
2. Trigger the resulting switch. 
3. Nothing happens (The webhook does not trigger).
 
```json
{
    "accessory": "HTTP-SWITCH",
    "name": "Printer Off Alert",
    "serialNumber": "SW007",
    "switchType": "stateless",
    "timeout": 1000,
    "onUrl": "https://maker.ifttt.com/trigger/homealert/json/with/key/***",
    "method": "POST",
    "headers": {
        "Content-Type": "application/json"
    },
    "body": {
        "value1": "Printer turned off",
        "value2": "",
        "value3": "https://cdn6.aptoide.com/imgs/6/b/8/6b80c88a03910f16ea0c7cf062952174_icon.png?w=256"
    }
}
```
The following _does_ work but I would love to use the simpler unencoded format.
```json
 {
    "accessory": "HTTP-SWITCH",
    "name": "Printer Off Alert",
    "serialNumber": "SW007",
    "switchType": "stateless",
    "timeout": 1000,
    "onUrl": "https://maker.ifttt.com/trigger/homealert/with/key/***?value1=%F0%9F%96%A8%20Printer%20turned%20off%20%F0%9F%96%A8&value2=&value3=https%3A%2F%2Fcdn6.aptoide.com%2Fimgs%2F6%2Fb%2F8%2F6b80c88a03910f16ea0c7cf062952174_icon.png%3Fw%3D256",
    "method": "POST"
   }
```

**Version** (output of `npm list -g homebridge homebridge-http-switch`)
![image](https://user-images.githubusercontent.com/1205471/133165438-e2d1f687-f842-4a52-8fd7-96597642717c.png)

* **Node.js Version**: 14.17.5
* **NPM Version**: 6.14.14
* **Homebridge Version**: 1.3.4
* **Homebridge Config UI X Version**: v4.41.2
* **Operating System**: Docker
* **Process Supervisor**: Docker 
* **Alpine Linux**: 3.12.7 
* **homebridge-http-switch:** v0.5.34

**Configuration**
```json
see above.
```

**Additional context**
Add any other context about the problem here.