Turn resource to plural form (#3061)

### What problem does this PR solve?

Turn resource to plural form

### Type of change
- [x] Refactoring

Co-authored-by: liuhua <10215101452@stu.ecun.edu.cn>

api/apps/sdk/dify_retrieval.py

@@ -22,7 +22,7 @@ from api.settings import retrievaler, kg_retrievaler, RetCode
 from api.utils.api_utils import validate_request, build_error_result, apikey_required
 
 
-@manager.route('/dify/retrievals', methods=['POST'])
+@manager.route('/dify/retrieval', methods=['POST'])
 @apikey_required
 @validate_request("knowledge_id", "query")
 def retrieval(tenant_id):

api/apps/sdk/doc.py

@@ -574,7 +574,7 @@ def update_chunk(tenant_id,dataset_id,document_id,chunk_id):
 
 
 
-@manager.route('/retrievals', methods=['POST'])
+@manager.route('/retrieval', methods=['POST'])
 @token_required
 def retrieval_test(tenant_id):
     req = request.json

api/http_api_reference.md

@@ -1169,14 +1169,14 @@ Failure:
 
 ## Retrieve chunks
 
-**GET** `/api/v1/retrievals`
+**GET** `/api/v1/retrieval`
 
 Retrieves chunks from specified datasets.
 
 ### Request
 
 - Method: POST
-- URL: `/api/v1/retrievals`
+- URL: `/api/v1/retrieval`
 - Headers:
   - `'content-Type: application/json'`
   - `'Authorization: Bearer {YOUR_API_KEY}'`
@@ -1197,7 +1197,7 @@ Retrieves chunks from specified datasets.
 
 ```bash
 curl --request POST \
-     --url http://{address}/api/v1/retrievals \
+     --url http://{address}/api/v1/retrieval \
      --header 'Content-Type: application/json' \
      --header 'Authorization: {YOUR_API_KEY}' \
      --data '