Use comment_id as when specified in the webhook payload

[stujo]

We had a bug which I think is caused by the use of the lastest_comment in the webhook. This change is intended to allow the webhook to specify a comment_id and to use that

The idea is that this is the trigger payload:

{   
  "ticket_id" : "{{ticket.id}}", 
  "topic_id": "{{ticket.external_id}}",
  "comment_id": "{{ticket.latest_comment.id}}",
  "email": "{{ticket.latest_comment.author.email}}",
 }