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/run_retrieval.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+set -euo pipefail
+
+SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
+REPO_ROOT="$(cd "${SCRIPT_DIR}/../.." && pwd)"
+
+: "${ZHIPU_AI_API_KEY:?ZHIPU_AI_API_KEY is required}"
+
+PYTHONPATH="${REPO_ROOT}/test" uv run -m benchmark retrieval \
+  --base-url http://127.0.0.1:9380 \
+  --allow-register \
+  --login-email "qa@infiniflow.org" \
+  --login-password "123" \
+  --bootstrap-llm \
+  --llm-factory ZHIPU-AI \
+  --llm-api-key "$ZHIPU_AI_API_KEY" \
+  --dataset-name "bench_dataset" \
+  --dataset-payload '{"name":"bench_dataset","embedding_model":"BAAI/bge-small-en-v1.5@Builtin"}' \
+  --document-path "${SCRIPT_DIR}/test_docs/Doc1.pdf" \
+  --document-path "${SCRIPT_DIR}/test_docs/Doc2.pdf" \
+  --document-path "${SCRIPT_DIR}/test_docs/Doc3.pdf" \
+  --question "What does RAG mean?" \
+  --iterations 10 \
+  --concurrency 8 \
+  --teardown