Migrate from utterance to giscus

> The intended way to leave a comment is supposed to be in a GitHub issue via utterance. However, it has been broken (at least on my blog) for some time now. Want to help me fix that? Here is one option: https://shipit.dev/posts/from-utterances-to-giscus.html

https://github.com/TysonMN/tysonmn.github.io/pull/50#issuecomment-2114028261