Feat: Benchmark CLI additions and documentation (#12536)

### What problem does this PR solve?

This PR adds a dedicated HTTP benchmark CLI for RAGFlow chat and
retrieval endpoints so we can measure latency/QPS.

### Type of change

- [x] Documentation Update
- [x] Other (please describe): Adds a CLI benchmarking tool for
chat/retrieval latency/QPS

---------

Co-authored-by: Liu An <asiro@qq.com>

test/benchmark/http_client.py

@@ -0,0 +1,112 @@
+import json
+from typing import Any, Dict, Optional, Tuple
+
+import requests
+
+
+class HttpClient:
+    def __init__(
+        self,
+        base_url: str,
+        api_version: str = "v1",
+        api_key: Optional[str] = None,
+        login_token: Optional[str] = None,
+        connect_timeout: float = 5.0,
+        read_timeout: float = 60.0,
+        verify_ssl: bool = True,
+    ) -> None:
+        self.base_url = base_url.rstrip("/")
+        self.api_version = api_version
+        self.api_key = api_key
+        self.login_token = login_token
+        self.connect_timeout = connect_timeout
+        self.read_timeout = read_timeout
+        self.verify_ssl = verify_ssl
+
+    def api_base(self) -> str:
+        return f"{self.base_url}/api/{self.api_version}"
+
+    def non_api_base(self) -> str:
+        return f"{self.base_url}/{self.api_version}"
+
+    def build_url(self, path: str, use_api_base: bool = True) -> str:
+        base = self.api_base() if use_api_base else self.non_api_base()
+        return f"{base}/{path.lstrip('/')}"
+
+    def _headers(self, auth_kind: Optional[str], extra: Optional[Dict[str, str]]) -> Dict[str, str]:
+        headers = {}
+        if auth_kind == "api" and self.api_key:
+            headers["Authorization"] = f"Bearer {self.api_key}"
+        elif auth_kind == "login" and self.login_token:
+            headers["Authorization"] = self.login_token
+        if extra:
+            headers.update(extra)
+        return headers
+
+    def request(
+        self,
+        method: str,
+        path: str,
+        *,
+        use_api_base: bool = True,
+        auth_kind: Optional[str] = "api",
+        headers: Optional[Dict[str, str]] = None,
+        json_body: Optional[Dict[str, Any]] = None,
+        data: Any = None,
+        files: Any = None,
+        params: Optional[Dict[str, Any]] = None,
+        stream: bool = False,
+    ) -> requests.Response:
+        url = self.build_url(path, use_api_base=use_api_base)
+        merged_headers = self._headers(auth_kind, headers)
+        timeout: Tuple[float, float] = (self.connect_timeout, self.read_timeout)
+        return requests.request(
+            method=method,
+            url=url,
+            headers=merged_headers,
+            json=json_body,
+            data=data,
+            files=files,
+            params=params,
+            timeout=timeout,
+            stream=stream,
+            verify=self.verify_ssl,
+        )
+
+    def request_json(
+        self,
+        method: str,
+        path: str,
+        *,
+        use_api_base: bool = True,
+        auth_kind: Optional[str] = "api",
+        headers: Optional[Dict[str, str]] = None,
+        json_body: Optional[Dict[str, Any]] = None,
+        data: Any = None,
+        files: Any = None,
+        params: Optional[Dict[str, Any]] = None,
+        stream: bool = False,
+    ) -> Dict[str, Any]:
+        response = self.request(
+            method,
+            path,
+            use_api_base=use_api_base,
+            auth_kind=auth_kind,
+            headers=headers,
+            json_body=json_body,
+            data=data,
+            files=files,
+            params=params,
+            stream=stream,
+        )
+        try:
+            return response.json()
+        except Exception as exc:
+            raise ValueError(f"Non-JSON response from {path}: {exc}") from exc
+
+    @staticmethod
+    def parse_json_bytes(raw: bytes) -> Dict[str, Any]:
+        try:
+            return json.loads(raw.decode("utf-8"))
+        except Exception as exc:
+            raise ValueError(f"Invalid JSON payload: {exc}") from exc