feat: add github copilot gpt-5-codex

[aemr3]

Added github copilot gpt-5-codex, its on vscode now.
Not sure about the context limits, feel free to update it.

cc: @fwang

[caozhiyuan]

@aemr3 {
"capabilities": {
"family": "gpt-5-codex",
"limits": {
"max_context_window_tokens": 200000,
"max_output_tokens": 64000,
"max_prompt_tokens": 128000,
"vision": {
"max_prompt_image_size": 3145728,
"max_prompt_images": 1,
"supported_media_types": ["image/jpeg", "image/png", "image/webp", "image/gif"]
}
},
"object": "model_capabilities",
"supports": {
"parallel_tool_calls": true,
"streaming": true,
"structured_outputs": true,
"tool_calls": true,
"vision": true
},
"tokenizer": "o200k_base",
"type": "chat"
},
"id": "gpt-5-codex",
"model_picker_category": "powerful",
"model_picker_enabled": true,
"name": "GPT-5-Codex (Preview)",
"object": "model",
"policy": {
"state": "enabled",
"terms": "Enable access to the latest GPT-5-Codex model from OpenAI. Learn more about how GitHub Copilot serves GPT-5-Codex."
},
"preview": true,
"supported_endpoints": ["/responses"],
"vendor": "OpenAI",
"version": "gpt-5-codex"
}