feat: add chat-api benchmark

[westbrook-ai]

• Adds a chat-api benchmark that adds new users and has them concurrently send chats to the Open WebUI API
• Renames channels benchmark to channels-api for consistency

[silentoplayz]

(owb-bench) ➜  open-webui-benchmark-suite git:(feat-ai-response-benchmark) ✗ owb run chat-api -m 10         

╔═══════════════════════════════════════════════════════════╗
║          Open WebUI Benchmark Suite v0.1.0                ║
║          Testing performance at scale                      ║
╚═══════════════════════════════════════════════════════════╝
    
╭───────────────────────────────── Benchmark ──────────────────────────────────╮
│ Running: Chat API Concurrency                                                │
│ Test concurrent AI chat performance via OpenAI API                           │
╰──────────────────────────────────────────────────────────────────────────────╯
⠴ Setting up... ━━━━╺━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━  10%
Running chat benchmark
Model: gpt-4o-mini
Concurrent users: 10
Requests per user: 5
Total requests: 50

⠏ Setting up... ━━━━╺━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━  10%
Completed: 50 | Errors: 0
  Complete! ━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━━ 100%
    Results: Chat API Concurrency    
┏━━━━━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━━┓
┃ Metric               ┃      Value ┃
┡━━━━━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━━┩
│ Max Concurrent Users │         10 │
│ Total Requests       │         50 │
│ Successful           │         50 │
│ Failed               │          0 │
│ Avg Response Time    │ 1037.44 ms │
│ P95 Response Time    │ 1621.63 ms │
│ P99 Response Time    │ 2097.03 ms │
│ Requests/sec         │       7.46 │
│ Error Rate           │      0.00% │
└──────────────────────┴────────────┘
Results written to: 
/home/g30/docker-projects/open-webui-benchmark-suite/results/chat_api_concurrenc
y_20260115_042735.json
CSV written to: 
/home/g30/docker-projects/open-webui-benchmark-suite/results/benchmark_results_2
0260115_042735.csv
Summary written to: 
/home/g30/docker-projects/open-webui-benchmark-suite/results/summary_20260115_04
2735.txt


╭──────────────────────────────────────────────────────────────────────────────╮
│ BENCHMARK SUITE COMPLETE                                                     │
╰──────────────────────────────────────────────────────────────────────────────╯
                             Final Results Summary                              
┏━━━━━━━━━━━━━━━━━━┳━━━━━━━━━━━┳━━━━━━━━━━┳━━━━━━━━━━┳━━━━━━━━━━┳━━━━━┳━━━━━━━━┓
┃ Benchmark        ┃ Max Users ┃ Requests ┃ Avg Time ┃ P95 Time ┃ RPS ┃ Errors ┃
┡━━━━━━━━━━━━━━━━━━╇━━━━━━━━━━━╇━━━━━━━━━━╇━━━━━━━━━━╇━━━━━━━━━━╇━━━━━╇━━━━━━━━┩
│ Chat API         │        10 │       50 │   1037ms │   1622ms │ 7.5 │   0.0% │
│ Concurrency      │           │          │          │          │     │        │
└──────────────────┴───────────┴──────────┴──────────┴──────────┴─────┴────────┘

LGTM!