MQTT - Doorbell Message never set back to 'false'
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**Describe The Problem:**
Firstly, I don't know if this is a bug or if it should be a feature request. Basically, I am using the MQTT topics to get metrics into prometheus/grafana. (I'm creating a dashboard for the number of vehicles driving/people walking/doorbell rings.) In the case of motion and smart detections, the MQTT topic is set to `true` when the event fires from the doorbell, and [is set back to `false` (and an MQTT event is fired) after the defined event timeout (`motionDuration`)](https://github.com/hjdhjd/homebridge-unifi-protect/blob/e6948831c5c206cb4ca8da847882606db8b522aa/src/protect-nvr-events.ts#L387-L409). The doorbell [does not set the topic back to false](https://github.com/hjdhjd/homebridge-unifi-protect/blob/e6948831c5c206cb4ca8da847882606db8b522aa/src/protect-nvr-events.ts#L488-L499). 

This specific inconsistency is where I am wondering if this is a bug, or a feature. :) 

**To Reproduce:**
With a G4 doorbell, Homebridge, MQTT enabled and publishing to a topic, and listening to a topic, ring the door bell and observe that the MQTT topic `unifi/protect/<Mac>/doorbell` is set to true and never reset. Trigger a motion event and observe that the MQTT topic `unifi/protect/<Mac>/motion` is set to true and then is set to false after the motionDuration timeout. Trigger a smart motion detection event (person or vehicle) and observe that the MQTT topic `unifi/protect/<Mac>/motion/smart/vehicle` is set to true and then is set to false after the motionDuration timeout.

**Logs:**
Logs from Homebridge are not applicable in this situation. 

```
Logs are not applicable or necessary in this situation.
```

**Homebridge Configuration:**

```json
        {
            "controllers": [
                {
                    "address": "192.168.x.x",
                    "mqttUrl": "mqtt://192.168.x.x",
                    "name": "UDM-Pro",
                    "password": "removed",
                    "refreshInterval": 10,
                    "username": "removed"
                }
            ],
            "motionDuration": 5,
            "platform": "UniFi Protect"
        },
```

**Screenshots:**
Doorbell MQTT:
(Notice the history tab - the topic is set to true and never set back to false.)
<img width="1536" alt="Screen Shot 2021-12-01 at 10 23 04 PM" src="https://user-images.githubusercontent.com/11429076/144357607-a53855a9-cb22-47fc-8ed6-2e7409b868a4.png">


Smart Vehicle MQTT Topic:
(Notice the history tab - after 5 seconds the topic value is set back to false.)
<img width="1527" alt="Screen Shot 2021-12-01 at 10 24 56 PM" src="https://user-images.githubusercontent.com/11429076/144357601-4d910c8a-d4d2-4b13-ba75-7fc70425d5ee.png">


**Environment:**

* **Homebridge Version:** 1.3.8
* **Node Version:** v14.16.1
* **Homebridge-UniFi-Protect Plugin Version:** v4.4.3
* **UniFi Protect Version:** 1.20.0
* **UniFi Protect Controller Type:** UDMP
* **UniFi Protect Controller Firmware Version:** 1.10.4
* **Apple Device and iOS / macOS / iPadOS / tvOS Version:** tested using 2019 MacBook Pro macOS 12.0.1. Homebridge runs on a 2014 Mac mini, macOS 12.0.1.
* **Operating System and OS Version:** macOS 12.0.1

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