[bug] Using litellm Message object not supported with instrumentation

[AdamRobertson-Cognasim]

Describe the bug
When using LiteLLMInstrumentor, you cannot use the Message objects provided by LiteLLM.
You have to use dictionaries.

This is unfortunate since we use the Message objects extensively.

To Reproduce

from phoenix.otel import register
import litellm 
from openinference.instrumentation.litellm import LiteLLMInstrumentor

# Setup tracer provider
tracer_provider = register(
    project_name="test",
    endpoint="http://localhost:6006/v1/traces",
    )

# Setup LiteLLM prebuilt instrument
LiteLLMInstrumentor().instrument(tracer_provider=tracer_provider)

# This works
model_response = litellm.completion(model='anthropic/claude-3-haiku-20240307',
                               messages=[{'role':'user',  'content':'hello'}])

# This throws an exception: "Object of type Message is not JSON serializable"
model_response = litellm.completion(model='anthropic/claude-3-haiku-20240307',
                               messages=[litellm.Message(role='user',  content='hello'])

Expected behavior
Calling litellm methods with litellm.Message objects and getting traces without exceptions.

Desktop

• OS: Windows
• Version openinference-instrumentation-litellm==0.1.11

[axiomofjoy]

Thanks for reporting @AdamRobertson-Cognasim! We will take a look.