Refactor: completion -> completions (#14584)

### What problem does this PR solve?

Keep only /completions, deprecated /completion

### Type of change

- [x] Refactoring

api/apps/backward_compat.py

@@ -403,14 +403,14 @@ async def deprecated_file_upload_info():
 @add_tenant_id_to_kwargs
 async def deprecated_agent_completions(agent_id, tenant_id=None):
     """
-    Deprecated: Use POST /api/v1/agents/chat/completion instead.
+    Deprecated: Use POST /api/v1/agents/chat/completions instead.
 
     Old path: POST /api/v1/agents/{agent_id}/completions
-    New path: POST /api/v1/agents/chat/completion
+    New path: POST /api/v1/agents/chat/completions
     """
     logging.warning(
         "API endpoint /api/v1/agents/%s/completions is deprecated. "
-        "Please use /api/v1/agents/chat/completion instead.",
+        "Please use /api/v1/agents/chat/completions instead.",
         agent_id,
     )
     return await agent_api.agent_chat_completion(tenant_id=tenant_id, agent_id=agent_id)

api/apps/restful_apis/agent_api.py

@@ -846,6 +846,7 @@ async def test_db_connection():
 
 
 @manager.route("/agents/chat/completion", methods=["POST"])  # noqa: F821
+@manager.route("/agents/chat/completions", methods=["POST"])  # noqa: F821
 @login_required
 @add_tenant_id_to_kwargs
 async def agent_chat_completion(tenant_id, agent_id=None):

api/apps/restful_apis/search_api.py

@@ -174,6 +174,7 @@ def delete_search(search_id):
 
 
 @manager.route("/searches/<search_id>/completion", methods=["POST"])  # noqa: F821
+@manager.route("/searches/<search_id>/completions", methods=["POST"])  # noqa: F821
 @login_required
 @validate_request("question")
 async def completion(search_id):

api/apps/services/canvas_replica_service.py

@@ -160,7 +160,7 @@ class CanvasReplicaService:
 
     @classmethod
     def load_for_run(cls, canvas_id: str, tenant_id: str, runtime_user_id: str):
-        """Load current runtime replica used by /completion."""
+        """Load current runtime replica used by /completions."""
         replica_key = cls._replica_key(canvas_id, str(tenant_id), str(runtime_user_id))
         return cls._read_payload(replica_key)