Make embedding generation go through inference (#606)

This PR does the following:
1) adds the ability to generate embeddings in all supported inference
providers.
2) Moves all the memory providers to use the inference API and improved
the memory tests to setup the inference stack correctly and use the
embedding models

This is a merge from #589 and #598

llama_stack/providers/remote/inference/vllm/vllm.py

@@ -29,6 +29,7 @@ from llama_stack.providers.utils.inference.openai_compat import (
 from llama_stack.providers.utils.inference.prompt_adapter import (
     chat_completion_request_to_prompt,
     completion_request_to_prompt,
+    content_has_media,
     convert_message_to_dict,
     request_has_media,
 )
@@ -203,4 +204,20 @@ class VLLMInferenceAdapter(Inference, ModelsProtocolPrivate):
         model_id: str,
         contents: List[InterleavedTextMedia],
     ) -> EmbeddingsResponse:
-        raise NotImplementedError()
+        model = await self.model_store.get_model(model_id)
+
+        kwargs = {}
+        assert model.model_type == ModelType.embedding_model
+        assert model.metadata.get("embedding_dimensions")
+        kwargs["dimensions"] = model.metadata.get("embedding_dimensions")
+        assert all(
+            not content_has_media(content) for content in contents
+        ), "VLLM does not support media for embeddings"
+        response = self.client.embeddings.create(
+            model=model.provider_resource_id,
+            input=[interleaved_text_media_as_str(content) for content in contents],
+            **kwargs,
+        )
+
+        embeddings = [data.embedding for data in response.data]
+        return EmbeddingsResponse(embeddings=embeddings)