chg: [dev] add user avatar

Author: VVX7

objects/facebook-account/definition.json

@@ -37,6 +37,12 @@
       "description": "Original URL location of the page (potentially malicious).",
       "misp-attribute": "url",
       "ui-priority": 1
+    },
+    "user-avatar": {
+      "description": "A user profile picture or avatar.",
+      "misp-attribute": "attachment",
+      "multiple": true,
+      "ui-priority": 1
     }
   },
   "description": "Facebook account.",