Ability to run lifecycle method on relationship update

Hi Richard, thanks for taking time to look into the issue.

I have listed the 2 models below. The relationship between users and presentation (~foo) is stored in a relational Postgres table.

I want to update numberOfPresentations every-time the relation between presentation and users is updated (users are added/removed as presenters/presentation is deleted).

Users model

{
   "kind": "collectionType",
   "collectionName": "users-permissions_user",
   "info": {
     "name": "user",
     "description": ""
   },
   "attributes": {
     "username": {
       "type": "string",
     },
     "name": {
       "type": "string"
     },
     "presentation": {
       "via": "presenters",
       "collection": "presentation"
     },
   "numberOfPresentations":{
       "type":"integer"
     }
   }
 }

Presentation model

{
  "kind": "collectionType",
  "collectionName": "presentation",
  "info": {
    "name": "presentation",
    "description": ""
  },
  "attributes": {
    "name": {
      "type": "string",
      "required": true
    },
    "presenters": {
      "plugin": "users-permissions",
      "collection": "user",
      "via": "presentation",
      "dominant": true
    }
  }
}