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/apis/models/models.py

@@ -4,6 +4,7 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
+from enum import Enum
 from typing import Any, Dict, List, Literal, Optional, Protocol, runtime_checkable
 
 from llama_models.schema_utils import json_schema_type, webmethod
@@ -20,6 +21,11 @@ class CommonModelFields(BaseModel):
     )
 
 
+class ModelType(Enum):
+    llm = "llm"
+    embedding_model = "embedding"
+
+
 @json_schema_type
 class Model(CommonModelFields, Resource):
     type: Literal[ResourceType.model.value] = ResourceType.model.value
@@ -34,12 +40,14 @@ class Model(CommonModelFields, Resource):
 
     model_config = ConfigDict(protected_namespaces=())
 
+    model_type: ModelType = Field(default=ModelType.llm)
+
 
 class ModelInput(CommonModelFields):
     model_id: str
     provider_id: Optional[str] = None
     provider_model_id: Optional[str] = None
-
+    model_type: Optional[ModelType] = ModelType.llm
     model_config = ConfigDict(protected_namespaces=())
 
 
@@ -59,6 +67,7 @@ class Models(Protocol):
         provider_model_id: Optional[str] = None,
         provider_id: Optional[str] = None,
         metadata: Optional[Dict[str, Any]] = None,
+        model_type: Optional[ModelType] = None,
     ) -> Model: ...
 
     @webmethod(route="/models/unregister", method="POST")