feat(api): remove List* response types and nils for get/list

TODO:
- make sure docstrings are refreshed as needed.
- make sure this passes tests.
- address a TODO in code (obsolete comment?)
- make sure client side still works.
- analyze if any providers need adjustments.

Signed-off-by: Ihar Hrachyshka <ihar.hrachyshka@gmail.com>

llama_stack/apis/telemetry/telemetry.py

@@ -103,6 +103,7 @@ class MetricInResponse(BaseModel):
     unit: Optional[str] = None
 
 
+# TODO: check what this comment is about
 # This is a short term solution to allow inference API to return metrics
 # The ideal way to do this is to have a way for all response types to include metrics
 # and all metric events logged to the telemetry API to be inlcuded with the response