turns out telescope is not ready to generate certificate in the ui process, a separate helper will be added for it, so remove this option for now.

Two stores are not a good idea to handle all the edge-cases since telescope supports certificates (or absence of these) per-session.

This way we can improve unload-certificate prompt. While here, move the cert handling in make_request().

While here replace GEMINI_URL_LEN with TOFU_URL_MAX_LEN to avoid a dependency on telescope.h. Ideally, we should move this stuff to another header that comes with less dependencies.