text: Title: OpenAI spec non-streaming response contains multiple `space` tokens
  Body: While serving a Llama-3 8B instruct LLM using OpenAI spec, the endpoint returns multiple spaces between words. It is because Llama generates contains space in the generated token. 
  
  We should use empty string to concat [OpenAI non-streaming chat content](https://github.com/Lightning-AI/LitServe/blob/81fffb66c6b8a95562317943e7de77dc1f2a5faf/src/litserve/specs/openai.py#L359-L364)
  
  ```
  for i, streaming_response in enumerate(pipe_responses):
              msgs = []
              tool_calls = None
              async for chat_msg in streaming_response:
                  chat_msg = json.loads(chat_msg)
                  logger.debug(chat_msg)
                  chat_msg = ChatMessage(**chat_msg)
                  msgs.append(chat_msg.content)
                  if chat_msg.tool_calls:
                      tool_calls = chat_msg.tool_calls
  
              # Is " " correct choice to concat with?
              content = " ".join(msgs)
              msg = {"role": "assistant", "content": content, "tool_calls": tool_calls}
  ```
  
  
  here is the llama response:
  <img width="543" alt="image" src="https://github.com/Lightning-AI/LitServe/assets/21018714/bc5c7c67-8f7a-4a98-a59b-0bcb29347df5">
  