fix: allowed_models config did not filter models (backport #4030) (#4223)

# What does this PR do?

closes #4022 

## Test Plan

ci w/ new tests<hr>This is an automatic backport of pull request #4030
done by [Mergify](https://mergify.com).

Co-authored-by: Matthew Farrellee <matt@cs.wisc.edu>
Co-authored-by: Ashwin Bharambe <ashwin.bharambe@gmail.com>

llama_stack/providers/utils/inference/model_registry.py

@@ -20,7 +20,7 @@ logger = get_logger(name=__name__, category="providers::utils")
 
 
 class RemoteInferenceProviderConfig(BaseModel):
-    allowed_models: list[str] | None = Field(  # TODO: make this non-optional and give a list() default
+    allowed_models: list[str] | None = Field(
         default=None,
         description="List of models that should be registered with the model registry. If None, all models are allowed.",
     )

llama_stack/providers/utils/inference/openai_mixin.py

@@ -82,9 +82,6 @@ class OpenAIMixin(NeedsRequestProviderData, ABC, BaseModel):
     # This is set in list_models() and used in check_model_availability()
     _model_cache: dict[str, Model] = {}
 
-    # List of allowed models for this provider, if empty all models allowed
-    allowed_models: list[str] = []
-
     # Optional field name in provider data to look for API key, which takes precedence
     provider_data_api_key_field: str | None = None
 
@@ -416,7 +413,7 @@ class OpenAIMixin(NeedsRequestProviderData, ABC, BaseModel):
         for provider_model_id in provider_models_ids:
             if not isinstance(provider_model_id, str):
                 raise ValueError(f"Model ID {provider_model_id} from list_provider_model_ids() is not a string")
-            if self.allowed_models and provider_model_id not in self.allowed_models:
+            if self.config.allowed_models is not None and provider_model_id not in self.config.allowed_models:
                 logger.info(f"Skipping model {provider_model_id} as it is not in the allowed models list")
                 continue
             if metadata := self.embedding_model_metadata.get(provider_model_id):