Use the latest Copilot Chat model schema, matching what is used in
VSCode, to get more data about available models than was previously
accessible. Replace hardcoded default model (gpt-4.1) with the default
model included in JSON. Other data like premium request multipliers
could be used in the future if Zed implements a way for models to
display additional details about themselves, such as with tooltips on
hover.
Release Notes:
- N/A
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Co-authored-by: Peter Tripp <peter@zed.dev>