refactor(api): rename "files" API to "artifacts"

The term "artifacts" better represents the purpose of this API, which
handles outputs generated by API executions, eventually stored objects
that can be of served by any storage interface (file, objects).

This aligns better with the industry convention of 'artifacts' (build
outputs, process results) rather than generic 'files'. 'files' would
be appropriate if the goal was to store and retrieve files purely.

Additionally, in our context, artifact is a better term since it will
handle:

* Data produced by SDG (Synthetic Data Generation) - as input
* Output of a trained model - as output

Signed-off-by: Sébastien Han <seb@redhat.com>

llama_stack/distribution/stack.py

@@ -13,12 +13,12 @@ from typing import Any
 import yaml
 
 from llama_stack.apis.agents import Agents
+from llama_stack.apis.artifacts import Artifacts
 from llama_stack.apis.batch_inference import BatchInference
 from llama_stack.apis.benchmarks import Benchmarks
 from llama_stack.apis.datasetio import DatasetIO
 from llama_stack.apis.datasets import Datasets
 from llama_stack.apis.eval import Eval
-from llama_stack.apis.files import Files
 from llama_stack.apis.inference import Inference
 from llama_stack.apis.inspect import Inspect
 from llama_stack.apis.models import Models
@@ -69,7 +69,7 @@ class LlamaStack(
     ToolGroups,
     ToolRuntime,
     RAGToolRuntime,
-    Files,
+    Artifacts,
 ):
     pass