Missing "deleted" field in MessageItem

[BernardoGiordano]

Hello. I'm opening this issue because the MessageItem class does not support is_deleted field that is sent from Instagram private messaging webhooks when a message is unsent.

Here is an example payload that shows the is_deleted field.

{
   "entry" : [
      {
         "id" : "page_id",
         "messaging" : [
            {
               "message" : {
                  "is_deleted" : true,
                  "mid" : "message_id"
               },
               "recipient" : {
                  "id" : "recipient_id"
               },
               "sender" : {
                  "id" : "sender_id"
               },
               "timestamp" : 1637138871850
            }
         ],
         "time" : 1637138871941
      }
   ],
   "object" : "instagram"
}