Support Codestral through Mistral API for inline predictions (to replace Supermaven?)

[dvcrn]

Since Supermaven is now in eternal "maintenance mode" after Cursor acquisition, it would be nice to have other state-of-the-art inline prediction options

Codestral is still one if not the best model for inline predictions with FITM, and can be used through their API which even includes a free tier: https://docs.mistral.ai/capabilities/code_generation/#fill-in-the-middle-endpoint

https://mistral.ai/news/codestral

[remorses]

PR to add Codestral support here: #34371