feat: add support for issue-metadata

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: jamacku

README.md

@@ -144,10 +144,21 @@ GitHub Action exposes following [outputs](https://docs.github.com/en/actions/usi
         ]
       }
     }
-  ]
+  ],
+  "metadata": [
+    {
+      "id": {
+        "key": "value"
+      }
+    }
+  ],
 }
 ```
 
+> [!NOTE]
+>
+> The `metadata` object holds all [issue-metadata](https://github.com/redhat-plumbers-in-action/issue-metadata) objects from the Pull Request comments. Issue-metadata have the following format: `<!-- <id> = {"key":"value"} -->`.
+
 ### metadata-file
 
 Relative path to JSON file containing Pull Request metadata object.