add embedding model by default to distribution templates (#617)

# What does this PR do?
Adds the sentence transformer provider and the `all-MiniLM-L6-v2`
embedding model to the default models to register in the run.yaml for
all providers.

## Test Plan
llama stack build --template together --image-type conda
llama stack run
~/.llama/distributions/llamastack-together/together-run.yaml

llama_stack/providers/inline/inference/meta_reference/inference.py

@@ -83,7 +83,7 @@ class MetaReferenceInferenceImpl(
 
     async def register_model(self, model: Model) -> Model:
         model = await self.model_registry_helper.register_model(model)
-        if model.model_type == ModelType.embedding_model:
+        if model.model_type == ModelType.embedding:
             self._load_sentence_transformer_model(model.provider_resource_id)
         return model