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/remote/memory/weaviate/weaviate.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 json
+import logging
 
 from typing import Any, Dict, List, Optional
 
@@ -22,6 +23,8 @@ from llama_stack.providers.utils.memory.vector_store import (
 
 from .config import WeaviateConfig, WeaviateRequestProviderData
 
+log = logging.getLogger(__name__)
+
 
 class WeaviateIndex(EmbeddingIndex):
     def __init__(self, client: weaviate.Client, collection_name: str):
@@ -69,10 +72,7 @@ class WeaviateIndex(EmbeddingIndex):
                 chunk_dict = json.loads(chunk_json)
                 chunk = Chunk(**chunk_dict)
             except Exception:
-                import traceback
-
-                traceback.print_exc()
-                print(f"Failed to parse document: {chunk_json}")
+                log.exception(f"Failed to parse document: {chunk_json}")
                 continue
 
             chunks.append(chunk)