always include the type field in requests

some endpoints, e.g. nvidia's hosted meta/llama-3.2-11b-vision-instruct, are strict about input schema. they require
messages to include the type field, i.e. {"text": ..., "type": "text"}.

the type field needs to be specified at construction time for it to be included in the request.

llama_stack/providers/utils/inference/openai_compat.py

@@ -527,6 +527,7 @@ async def convert_message_to_openai_dict_new(message: Message | Dict) -> OpenAIC
         elif isinstance(content, TextContentItem):
             return OpenAIChatCompletionContentPartTextParam(
                 text=content.text,
+                type="text",
             )
         elif isinstance(content, ImageContentItem):
             return OpenAIChatCompletionContentPartImageParam(