feat: support filters in file search (#2472)

# What does this PR do?
Move to use vector_stores.search for file search tool in Responses,
which supports filters.

closes #2435 

## Test Plan
Added e2e test with fitlers.
myenv ❯ llama stack run llama_stack/templates/fireworks/run.yaml

pytest -sv tests/verifications/openai_api/test_responses.py \
  -k 'file_search and filters' \
  --base-url=http://localhost:8321/v1/openai/v1 \
  --model=meta-llama/Llama-3.3-70B-Instruct

docs/_static/llama-stack-spec.yaml

@@ -5179,7 +5179,7 @@ components:
               type: number
               default: 0.0
           additionalProperties: false
-          title: FileSearchRankingOptions
+          title: SearchRankingOptions
       additionalProperties: false
       required:
         - type
@@ -9408,14 +9408,13 @@ components:
             Maximum number of results to return (1 to 50 inclusive, default 10).
         ranking_options:
           type: object
-          additionalProperties:
-            oneOf:
-              - type: 'null'
-              - type: boolean
-              - type: number
-              - type: string
-              - type: array
-              - type: object
+          properties:
+            ranker:
+              type: string
+            score_threshold:
+              type: number
+              default: 0.0
+          additionalProperties: false
           description: >-
             Ranking options for fine-tuning the search results.
         rewrite_query: