fix: stress test setup process and report structure workflow for Dify 1.15.0+

[Blackoutta]

Summary

This PR updates the stress-test setup and SSE benchmark scripts so they can run smoothly on Dify 1.15.0+ source deployments.

It fixes the setup flow around current console authentication, initialized-instance handling, plugin installation responses, workflow import warnings, setup step failure propagation, Locust dependency conflicts, and per-run report output.

Fixes #38193.

Changes

• Encode console login passwords like the web client and persist the auth/CSRF cookies returned by login.
• Send console auth headers and cookies from shared config helpers.
• Support both brand-new Dify instances and already-initialized instances with admin credentials from environment variables.
• Make setup scripts return non-zero on real failures so setup_all.py stops at the root cause.
• Treat already-installed/no-task plugin install responses as non-blocking when no error code is present.
• Accept workflow imports that complete with warnings when an app_id is returned.
• Run Locust through uvx --from locust locust to avoid API dependency conflicts.
• Group each benchmark run's reports under a timestamped directory and print the custom SSE metrics JSON path.
• Add focused tests for the setup script behavior.

Video

fix_stress_test.mp4

Validation

• uv run --project api pytest scripts/stress-test/test_setup_scripts.py
• uv run --project api python -m py_compile scripts/stress-test/setup_all.py scripts/stress-test/test_setup_scripts.py
• bash -n scripts/stress-test/run_locust_stress_test.sh
• uvx --from locust locust -f scripts/stress-test/sse_benchmark.py --list