assistant: Add model names in alternative inline tooltips (#20350)

Closes https://github.com/zed-industries/zed/issues/18826

This PR adds the model name to the tooltips on the alternative inline
assistant icon buttons. The default model should be the first, so every
other one set as an alternative appears after.


https://github.com/user-attachments/assets/46faccaa-447c-45a4-b927-49ea3c4f3be1


Release Notes:

- Improve knowledge of which model is used when with alternative inline
models turned on