Add `<image_placeholder>` token

tokenizer.json

@@ -5348,6 +5348,15 @@
       "rstrip": false,
       "normalized": false,
       "special": true
+    },
+    {
+      "id": 100594,
+      "content": "<image_placeholder>",
+      "single_word": false,
+      "lstrip": false,
+      "rstrip": false,
+      "normalized": false,
+      "special": true
     }
   ],
   "normalizer": {