feat: add a configurable category-based logger (#1352)

A self-respecting server needs good observability which starts with
configurable logging. Llama Stack had little until now. This PR adds a
`logcat` facility towards that. Callsites look like:

```python
logcat.debug("inference", f"params to ollama: {params}")
```

- the first parameter is a category. there is a static list of
categories in `llama_stack/logcat.py`
- each category can be associated with a log-level which can be
configured via the `LLAMA_STACK_LOGGING` env var.
- a value `LLAMA_STACK_LOGGING=inference=debug;server=info"` does the
obvious thing. there is a special key called `all` which is an alias for
all categories

## Test Plan

Ran with `LLAMA_STACK_LOGGING="all=debug" llama stack run fireworks` and
saw the following:


![image](https://github.com/user-attachments/assets/d24b95ab-3941-426c-9ea0-a4c62542e6f0)

Hit it with a client-sdk test case and saw this:


![image](https://github.com/user-attachments/assets/3fee8c6c-986e-4125-a09c-f5dc019682e2)

llama_stack/distribution/start_stack.sh

@@ -98,9 +98,8 @@ case "$env_type" in
   *)
 esac
 
-set -x
-
 if [[ "$env_type" == "venv" || "$env_type" == "conda" ]]; then
+    set -x
     $PYTHON_BINARY -m llama_stack.distribution.server.server \
     --yaml-config "$yaml_config" \
     --port "$port" \
@@ -142,6 +141,8 @@ elif [[ "$env_type" == "container" ]]; then
         version_tag=$(curl -s $URL | jq -r '.info.version')
     fi
 
+    set -x
+
     $CONTAINER_BINARY run $CONTAINER_OPTS -it \
     -p $port:$port \
     $env_vars \