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/utils/kvstore/postgres/postgres.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
 from datetime import datetime
 from typing import List, Optional
 
@@ -13,6 +14,8 @@ from psycopg2.extras import DictCursor
 from ..api import KVStore
 from ..config import PostgresKVStoreConfig
 
+log = logging.getLogger(__name__)
+
 
 class PostgresKVStoreImpl(KVStore):
     def __init__(self, config: PostgresKVStoreConfig):
@@ -43,9 +46,8 @@ class PostgresKVStoreImpl(KVStore):
                 """
             )
         except Exception as e:
-            import traceback
 
-            traceback.print_exc()
+            log.exception("Could not connect to PostgreSQL database server")
             raise RuntimeError("Could not connect to PostgreSQL database server") from e
 
     def _namespaced_key(self, key: str) -> str: