use logging instead of prints (#499)

# What does this PR do?

This PR moves all print statements to use logging. Things changed:
- Had to add `await start_trace("sse_generator")` to server.py to
actually get tracing working. else was not seeing any logs
- If no telemetry provider is provided in the run.yaml, we will write to
stdout
- by default, the logs are going to be in JSON, but we expose an option
to configure to output in a human readable way.

llama_stack/providers/inline/agents/meta_reference/safety.py

@@ -5,14 +5,16 @@
 # the root directory of this source tree.
 
 import asyncio
+import logging
 
 from typing import List
 
 from llama_models.llama3.api.datatypes import Message
-from termcolor import cprint
 
 from llama_stack.apis.safety import *  # noqa: F403
 
+log = logging.getLogger(__name__)
+
 
 class SafetyException(Exception):  # noqa: N818
     def __init__(self, violation: SafetyViolation):
@@ -51,7 +53,4 @@ class ShieldRunnerMixin:
             if violation.violation_level == ViolationLevel.ERROR:
                 raise SafetyException(violation)
             elif violation.violation_level == ViolationLevel.WARN:
-                cprint(
-                    f"[Warn]{identifier} raised a warning",
-                    color="red",
-                )
+                log.warning(f"[Warn]{identifier} raised a warning")