[FIX] mail_tracking: process sent events

Up until now, the `sent` event type was never processed, probably because it "made no sense", as an unsent email would never trigger an event.

However, it makes sense to process it because you may have a local relay that transmits mails over to the mail provider. In those circumstances, you should have 2 "sent" events (one from the relay and another one from the provider).

Also marked some useless parts of code for removal.

@Tecnativa TT32365

mail_tracking/controllers/main.py

@@ -41,6 +41,7 @@ class MailTrackingController(MailController, DiscussController):
             "ua_family": request.user_agent.browser or False,
         }
 
+    # TODO Remove useless controller
     @http.route(
         [
             "/mail/tracking/all/<string:db>",

mail_tracking/models/mail_tracking_email.py

@@ -372,6 +372,7 @@ class MailTrackingEmail(models.Model):
                 _logger.debug("Concurrent event '%s' discarded", event_type)
         return event_ids
 
+    # TODO Remove useless method
     @api.model
     def event_process(self, request, post, metadata, event_type=None):
         # Generic event process hook, inherit it and

mail_tracking/models/mail_tracking_event.py

@@ -119,6 +119,10 @@ class MailTrackingEvent(models.Model):
         )
         return self._process_data(tracking_email, metadata, event_type, state)
 
+    @api.model
+    def process_sent(self, tracking_email, metadata):
+        return self._process_status(tracking_email, metadata, "sent", "sent")
+
     @api.model
     def process_delivered(self, tracking_email, metadata):
         return self._process_status(tracking_email, metadata, "delivered", "delivered")