Update support for langfuse metadata

- Added ability to set trace release, version, metadata
- Added ability to update fields during a trace continuation
- Added ability to update input and output during a trace continuation
- Wrote new test for verifying metadata is set correctly
- Small improvement to setting secret boolean, prevent unnecessary literal_eval
- Small improvements to langfuse tests

litellm/utils.py

@@ -9363,7 +9363,7 @@ def get_secret(
         else:
             secret = os.environ.get(secret_name)
             try:
-                secret_value_as_bool = ast.literal_eval(secret)
+                secret_value_as_bool = ast.literal_eval(secret) if secret is not None else None
                 if isinstance(secret_value_as_bool, bool):
                     return secret_value_as_bool
                 else: