chore: add storage sane defaults (#4182)

# What does this PR do?

since `StackRunConfig` requires certain parts of `StorageConfig`, it'd
probably make sense to template in some defaults that will "just work"
for most usecases

specifically introduce`ServerStoresConfig` defaults for inference,
metadata, conversations and prompts. We already actually funnel in
defaults for these sections ad-hoc throughout the codebase

additionally set some `backends` defaults for the `StorageConfig`.

This will alleviate some weirdness for `--providers` for run/list-deps
and also some work I have to better align our list-deps/run datatypes

---------

Signed-off-by: Charlie Doern <cdoern@redhat.com>

tests/unit/conversations/test_conversations.py

@@ -38,6 +38,9 @@ async def service():
             },
             stores=ServerStoresConfig(
                 conversations=SqlStoreReference(backend="sql_test", table_name="openai_conversations"),
+                metadata=None,
+                inference=None,
+                prompts=None,
             ),
         )
         register_sqlstore_backends({"sql_test": storage.backends["sql_test"]})
@@ -142,6 +145,9 @@ async def test_policy_configuration():
             },
             stores=ServerStoresConfig(
                 conversations=SqlStoreReference(backend="sql_test", table_name="openai_conversations"),
+                metadata=None,
+                inference=None,
+                prompts=None,
             ),
         )
         register_sqlstore_backends({"sql_test": storage.backends["sql_test"]})

tests/unit/core/test_stack_validation.py

@@ -10,8 +10,9 @@ from unittest.mock import AsyncMock
 
 import pytest
 
-from llama_stack.core.datatypes import QualifiedModel, SafetyConfig, StackRunConfig, StorageConfig, VectorStoresConfig
+from llama_stack.core.datatypes import QualifiedModel, SafetyConfig, StackRunConfig, VectorStoresConfig
 from llama_stack.core.stack import validate_safety_config, validate_vector_stores_config
+from llama_stack.core.storage.datatypes import ServerStoresConfig, StorageConfig
 from llama_stack_api import Api, ListModelsResponse, ListShieldsResponse, Model, ModelType, Shield
 
 
@@ -21,7 +22,15 @@ class TestVectorStoresValidation:
         run_config = StackRunConfig(
             image_name="test",
             providers={},
-            storage=StorageConfig(backends={}, stores={}),
+            storage=StorageConfig(
+                backends={},
+                stores=ServerStoresConfig(
+                    metadata=None,
+                    inference=None,
+                    conversations=None,
+                    prompts=None,
+                ),
+            ),
             vector_stores=VectorStoresConfig(
                 default_provider_id="faiss",
                 default_embedding_model=QualifiedModel(
@@ -41,7 +50,15 @@ class TestVectorStoresValidation:
         run_config = StackRunConfig(
             image_name="test",
             providers={},
-            storage=StorageConfig(backends={}, stores={}),
+            storage=StorageConfig(
+                backends={},
+                stores=ServerStoresConfig(
+                    metadata=None,
+                    inference=None,
+                    conversations=None,
+                    prompts=None,
+                ),
+            ),
             vector_stores=VectorStoresConfig(
                 default_provider_id="faiss",
                 default_embedding_model=QualifiedModel(