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/server/server.py

@@ -46,6 +46,10 @@ from llama_stack.distribution.stack import (
     replace_env_vars,
     validate_env_pair,
 )
+from llama_stack.providers.inline.meta_reference.telemetry.console import (
+    ConsoleConfig,
+    ConsoleTelemetryImpl,
+)
 
 from .endpoints import get_all_api_endpoints
 
@@ -196,7 +200,6 @@ def handle_sigint(app, *args, **kwargs):
 async def lifespan(app: FastAPI):
     print("Starting up")
     yield
-
     print("Shutting down")
     for impl in app.__llama_stack_impls__.values():
         await impl.shutdown()
@@ -214,6 +217,7 @@ async def maybe_await(value):
 
 
 async def sse_generator(event_gen):
+    await start_trace("sse_generator")
     try:
         event_gen = await event_gen
         async for item in event_gen:
@@ -333,7 +337,7 @@ def main():
     print("Run configuration:")
     print(yaml.dump(config.model_dump(), indent=2))
 
-    app = FastAPI()
+    app = FastAPI(lifespan=lifespan)
 
     try:
         impls = asyncio.run(construct_stack(config))
@@ -342,6 +346,8 @@ def main():
 
     if Api.telemetry in impls:
         setup_logger(impls[Api.telemetry])
+    else:
+        setup_logger(ConsoleTelemetryImpl(ConsoleConfig()))
 
     all_endpoints = get_all_api_endpoints()