Replace Message Bridge with nRF Cloud Message Routing

The nRF Cloud Message Routing now sends AWS Thingy Shadow documents. This is much more convenient compared to the current implementation which requires the backend to poll the device state regularly.

The webhook now receives a message that is a copy of the `$aws/things//shadow/update/documents` message.

In the example below this was the shadow update: `{"reported": { "foo": "bar" }}`

```json
{
"type": "device.messages",
"messages": [
{
"teamId": "",
"deviceId": "",
"messageId": "251cd7a1-23a4-422d-be14-1aafd209e75b",
"topic": "$aws/things//shadow/update/documents",
"message": {
"previous": {
"state": {
"desired": {
"nrfcloud_mqtt_topic_prefix": "prod//",
"pairing": {
"state": "paired",
"topics": {
"d2c": "prod//m/d//d2c",
"c2d": "prod//m/d//+/r"
}
}
}
},
"metadata": {
"desired": {
"nrfcloud_mqtt_topic_prefix": { "timestamp": 1723215415 },
"pairing": {
"state": { "timestamp": 1723215415 },
"topics": {
"d2c": { "timestamp": 1723215415 },
"c2d": { "timestamp": 1723215415 }
}
}
}
},
"version": 1
},
"current": {
"state": {
"desired": {
"nrfcloud_mqtt_topic_prefix": "prod//",
"pairing": {
"state": "paired",
"topics": {
"d2c": "prod//m/d//d2c",
"c2d": "prod//m/d//+/r"
}
}
},
"reported": { "foo": "bar" }
},
"metadata": {
"desired": {
"nrfcloud_mqtt_topic_prefix": { "timestamp": 1723215415 },
"pairing": {
"state": { "timestamp": 1723215415 },
"topics": {
"d2c": { "timestamp": 1723215415 },
"c2d": { "timestamp": 1723215415 }
}
}
},
"reported": { "foo": { "timestamp": 1749799965 } }
},
"version": 2
},
"timestamp": 1749799965
},
"receivedAt": "2025-06-13T07:32:45.090Z"
}
],
"timestamp": "2025-06-13T07:32:45.145971775Z"
}
```