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/apis/common/responses.py

@@ -4,8 +4,6 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
-from typing import Any
-
 from pydantic import BaseModel
 
 from llama_stack.schema_utils import json_schema_type
@@ -19,5 +17,5 @@ class PaginatedResponse(BaseModel):
     :param has_more: Whether there are more items available after this set
     """
 
-    data: list[dict[str, Any]]
+    data: list
     has_more: bool