fix(haystack): update EnhancedJSONEncoder to use model_dump_json

Author: ryanamannion

packages/opentelemetry-instrumentation-haystack/opentelemetry/instrumentation/haystack/utils.py

@@ -15,6 +15,8 @@ def default(self, o):
             return dataclasses.asdict(o)
         if hasattr(o, "to_json"):
             return o.to_json()
+        if hasattr(o, "model_dump_json"):
+            return o.model_dump_json()
         return super().default(o)