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/agents/meta_reference/rag/context_retriever.py

@@ -10,8 +10,6 @@ from jinja2 import Template
 from llama_models.llama3.api import *  # noqa: F403
 
 
-from termcolor import cprint  # noqa: F401
-
 from llama_stack.apis.agents import (
     DefaultMemoryQueryGeneratorConfig,
     LLMMemoryQueryGeneratorConfig,
@@ -36,7 +34,6 @@ async def generate_rag_query(
         query = await llm_rag_query_generator(config, messages, **kwargs)
     else:
         raise NotImplementedError(f"Unsupported memory query generator {config.type}")
-    # cprint(f"Generated query >>>: {query}", color="green")
     return query