fix: pull ollama embedding model if necessary (#1209)

Embedding models are tiny and can be pulled on-demand. Let's do that so
the user doesn't have to do "yet another thing" to get themselves set
up.

Thanks @hardikjshah for the suggestion.

Also fixed a build dependency miss (TODO: distro_codegen needs to
actually check that the build template contains all providers mentioned
for the run.yaml file)

## Test Plan 

First run `ollama rm all-minilm:latest`. 

Run `llama stack build --template ollama && llama stack run ollama --env
INFERENCE_MODEL=llama3.2:3b-instruct-fp16`. See that it outputs a
"Pulling embedding model `all-minilm:latest`" output and the stack
starts up correctly. Verify that `ollama list` shows the model is
correctly downloaded.

llama_stack/providers/remote/inference/ollama/ollama.py

@@ -281,6 +281,8 @@ class OllamaInferenceAdapter(Inference, ModelsProtocolPrivate):
 
     async def register_model(self, model: Model) -> Model:
         if model.model_type == ModelType.embedding:
+            log.info(f"Pulling embedding model `{model.provider_resource_id}` if necessary...")
+            await self.client.pull(model.provider_resource_id)
             response = await self.client.list()
         else:
             response = await self.client.ps()