feat(verification): various improvements (#1921)

# What does this PR do?
- provider and their models now live in config.yaml
- better distinguish different cases within a test
- add model key to surface provider's model_id
- include example command to rerun single test case

## Test Plan
<img width="1173" alt="image"
src="https://github.com/user-attachments/assets/b414baf0-c768-451f-8c3b-c2905cf36fac"
/>

tests/verifications/openai_api/fixtures/load.py

@@ -0,0 +1,16 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the terms described in the LICENSE file in
+# the root directory of this source tree.
+
+from pathlib import Path
+
+import yaml
+
+
+def load_test_cases(name: str):
+    fixture_dir = Path(__file__).parent / "test_cases"
+    yaml_path = fixture_dir / f"{name}.yaml"
+    with open(yaml_path, "r") as f:
+        return yaml.safe_load(f)