[Obs AI Assistant] Add OpenAI models to the performance matrix (#3675)

Closes elastic/obs-ai-assistant-team#342
[Obs AI Assistant] Add OpenAI models (gpt-oss-120b and gpt-oss-20b) in
the LLM performance matrix

---------

Co-authored-by: Viduni Wickramarachchi <[email protected]>

Author: arturoliduena

solutions/observability/llm-performance-matrix.md

@@ -54,6 +54,8 @@ Models you can [deploy and manage yourself](/solutions/observability/connect-to-
 | Meta | **Llama-3.3-70B-Instruct** | Excellent | Good | Great | Excellent | Excellent | Good | Good | Excellent |
 | Mistral | **Mistral-Small-3.2-24B-Instruct-2506** | Excellent | Poor | Great | Great | Excellent | Good | Good | Excellent |
 | Alibaba Cloud | **Qwen2.5-72b-Instruct** | Excellent | Good | Great | Excellent | Excellent | Good | Good | Excellent |
+| OpenAI | **gpt-oss-20b** | Poor | Poor | Great | Poor | Good | Poor | Good | Good |
+| OpenAI | **gpt-oss-120b** | Excellent | Poor | Great | Great | Excellent | Good | Good | Excellent |
 
 ::::{note}
 `Llama-3.3-70B-Instruct` and `Qwen2.5-72b-Instruct` were tested with simulated function calling.