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/console.py

@@ -4,8 +4,11 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
+import json
 from typing import Optional
 
+from .config import LogFormat
+
 from llama_stack.apis.telemetry import *  # noqa: F403
 from .config import ConsoleConfig
 
@@ -38,7 +41,11 @@ class ConsoleTelemetryImpl(Telemetry):
 
         span_name = ".".join(names) if names else None
 
-        formatted = format_event(event, span_name)
+        if self.config.log_format == LogFormat.JSON:
+            formatted = format_event_json(event, span_name)
+        else:
+            formatted = format_event_text(event, span_name)
+
         if formatted:
             print(formatted)
 
@@ -69,7 +76,7 @@ SEVERITY_COLORS = {
 }
 
 
-def format_event(event: Event, span_name: str) -> Optional[str]:
+def format_event_text(event: Event, span_name: str) -> Optional[str]:
     timestamp = event.timestamp.strftime("%H:%M:%S.%f")[:-3]
     span = ""
     if span_name:
@@ -87,3 +94,23 @@ def format_event(event: Event, span_name: str) -> Optional[str]:
         return None
 
     return f"Unknown event type: {event}"
+
+
+def format_event_json(event: Event, span_name: str) -> Optional[str]:
+    base_data = {
+        "timestamp": event.timestamp.isoformat(),
+        "trace_id": event.trace_id,
+        "span_id": event.span_id,
+        "span_name": span_name,
+    }
+
+    if isinstance(event, UnstructuredLogEvent):
+        base_data.update(
+            {"type": "log", "severity": event.severity.name, "message": event.message}
+        )
+        return json.dumps(base_data)
+
+    elif isinstance(event, StructuredLogEvent):
+        return None
+
+    return json.dumps({"error": f"Unknown event type: {event}"})