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/meta_reference/telemetry/config.py

@@ -4,10 +4,18 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
+from enum import Enum
+
 from llama_models.schema_utils import json_schema_type
 
 from pydantic import BaseModel
 
 
+class LogFormat(Enum):
+    TEXT = "text"
+    JSON = "json"
+
+
 @json_schema_type
-class ConsoleConfig(BaseModel): ...
+class ConsoleConfig(BaseModel):
+    log_format: LogFormat = LogFormat.JSON