revert: "chore(cleanup)!: remove tool_runtime.rag_tool" (#3877)

Reverts llamastack/llama-stack#3871

This PR broke RAG (even from Responses -- there _is_ a dependency)

llama_stack/distributions/dell/run-with-safety.yaml

@@ -87,6 +87,8 @@ providers:
     config:
       api_key: ${env.TAVILY_SEARCH_API_KEY:=}
       max_results: 3
+  - provider_id: rag-runtime
+    provider_type: inline::rag-runtime
 storage:
   backends:
     kv_default:
@@ -131,6 +133,8 @@ registered_resources:
   tool_groups:
   - toolgroup_id: builtin::websearch
     provider_id: brave-search
+  - toolgroup_id: builtin::rag
+    provider_id: rag-runtime
 server:
   port: 8321
 telemetry: