simplify authenticate()

[romainfrancois]

closes #17

This way we get the same error as if the key was wrong:

mistral.ai::chat("hello")
#> Error in `mistral.ai::chat()`:
#> ✖ with endpoint <https://api.mistral.ai/v1/models>
#> ℹ Make sure your api key is valid <https://console.mistral.ai/api-keys/>
#> ℹ And set the `MISTRAL_API_KEY` environment variable
#> ℹ Perhaps using `usethis::edit_r_environ()`
#> Caused by error in `req_perform()` at mistral.ai/R/httr2.R:22:3:
#> ! HTTP 401 Unauthorized.

^{Created on 2024-03-09 with reprex v2.1.0}

[JamesHWade]

I like this simplification. As a convenience feature, what about making usethis::edit_r_environ() run when the user clicks it?

[romainfrancois]

It's already the case with i = "Perhaps using {.fn usethis::edit_r_environ}" curtosy of cli inline markup