Add version to hassfest for custom integrations (#45523)

Co-authored-by: Paulus Schoutsen <balloob@gmail.com>

script/hassfest/model.py

@@ -74,6 +74,11 @@ class Integration:
         """Integration domain."""
         return self.path.name
 
+    @property
+    def core(self) -> bool:
+        """Core integration."""
+        return self.path.as_posix().startswith("homeassistant/components")
+
     @property
     def disabled(self) -> Optional[str]:
         """List of disabled."""