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/distribution/stack.py

@@ -4,6 +4,7 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
+import logging
 import os
 from pathlib import Path
 from typing import Any, Dict
@@ -40,6 +41,8 @@ from llama_stack.distribution.store.registry import create_dist_registry
 from llama_stack.providers.datatypes import Api
 
 
+log = logging.getLogger(__name__)
+
 LLAMA_STACK_API_VERSION = "alpha"
 
 
@@ -93,11 +96,11 @@ async def register_resources(run_config: StackRunConfig, impls: Dict[Api, Any]):
 
         method = getattr(impls[api], list_method)
         for obj in await method():
-            print(
+            log.info(
                 f"{rsrc.capitalize()}: {colored(obj.identifier, 'white', attrs=['bold'])} served by {colored(obj.provider_id, 'white', attrs=['bold'])}",
             )
 
-    print("")
+    log.info("")
 
 
 class EnvVarError(Exception):