Document eligible OpenAI models for parse_via_gpt_vision flow webhook

[AmishaBisht]

Eligible models to publish (must be vision-capable)

• gpt-5.1 — GPT-5 family; current default
• gpt-5 — GPT-5 family
• gpt-5-mini — GPT-5 family
• gpt-4.1 — GPT-4.1 family
• gpt-4.1-mini — GPT-4.1 family
• gpt-4.1-nano — GPT-4.1 family
• gpt-4o — original vision workhorse
• gpt-4o-mini
• gpt-4-turbo — vision-capable since 2024-04
• o1, o3, o4-mini — reasoning models with vision; webhook doesn't send temperature, so no extra param conflict