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/watsonx/build.yaml

@@ -23,6 +23,7 @@ distribution_spec:
     tool_runtime:
     - provider_type: remote::brave-search
     - provider_type: remote::tavily-search
+    - provider_type: inline::rag-runtime
     - provider_type: remote::model-context-protocol
     files:
     - provider_type: inline::localfs

llama_stack/distributions/watsonx/run.yaml

@@ -83,6 +83,8 @@ providers:
     config:
       api_key: ${env.TAVILY_SEARCH_API_KEY:=}
       max_results: 3
+  - provider_id: rag-runtime
+    provider_type: inline::rag-runtime
   - provider_id: model-context-protocol
     provider_type: remote::model-context-protocol
   files:
@@ -123,6 +125,8 @@ registered_resources:
   tool_groups:
   - toolgroup_id: builtin::websearch
     provider_id: tavily-search
+  - toolgroup_id: builtin::rag
+    provider_id: rag-runtime
 server:
   port: 8321
 telemetry:

llama_stack/distributions/watsonx/watsonx.py

@@ -33,6 +33,7 @@ def get_distribution_template(name: str = "watsonx") -> DistributionTemplate:
         "tool_runtime": [
             BuildProvider(provider_type="remote::brave-search"),
             BuildProvider(provider_type="remote::tavily-search"),
+            BuildProvider(provider_type="inline::rag-runtime"),
             BuildProvider(provider_type="remote::model-context-protocol"),
         ],
         "files": [BuildProvider(provider_type="inline::localfs")],
@@ -49,6 +50,10 @@ def get_distribution_template(name: str = "watsonx") -> DistributionTemplate:
             toolgroup_id="builtin::websearch",
             provider_id="tavily-search",
         ),
+        ToolGroupInput(
+            toolgroup_id="builtin::rag",
+            provider_id="rag-runtime",
+        ),
     ]
 
     files_provider = Provider(