feat: add refresh_models support to inference adapters (default: false) (#3719)

# What does this PR do?

inference adapters can now configure `refresh_models: bool` to control
periodic model listing from their providers

BREAKING CHANGE: together inference adapter default changed. previously
always refreshed, now follows config.

addresses "models: refresh" on #3517

## Test Plan

ci w/ new tests

llama_stack/providers/utils/inference/model_registry.py

@@ -24,6 +24,10 @@ class RemoteInferenceProviderConfig(BaseModel):
         default=None,
         description="List of models that should be registered with the model registry. If None, all models are allowed.",
     )
+    refresh_models: bool = Field(
+        default=False,
+        description="Whether to refresh models periodically from the provider",
+    )
 
 
 # TODO: this class is more confusing than useful right now. We need to make it

llama_stack/providers/utils/inference/openai_mixin.py

@@ -484,7 +484,7 @@ class OpenAIMixin(NeedsRequestProviderData, ABC, BaseModel):
         return model in self._model_cache
 
     async def should_refresh_models(self) -> bool:
-        return False
+        return self.config.refresh_models
 
     #
     # The model_dump implementations are to avoid serializing the extra fields,