Migration of the REST payload from legacy to v1 - FCM

legacy.json

{
    "to": "token o topic",
    "priority": "high",
    "notification": {
        "title": "Title of the notification",
        "body": "Description of the notification",
        "android_channel_id": "Android channel"
    },
    "data": {
        "field_1": "Some extra data"
    }
}

v1.jsonc

{
    "message": {
        "token": "token", // or "topic" if we want to send for a topic
        "notification": {
            "title": "Title of the notification",
            "body": "Description of the notification"
        },
        "android": {
            "priority": "high",
            "notification": {
                "channel_id": "Android channel"
            }
        },
        "data": {
            "field_1": "Some extra data"
        }
    },
}