Use fancy HTML-enabled Issue Form Templates for issues

Structured forms can give a more polished bug report / feature request experience, with drop down menus, separate text fields and more.

This can be seen in the `cargo` repo, check out the [underlying issue templates](https://github.com/rust-lang/cargo/tree/master/.github/ISSUE_TEMPLATE) to see how it's done.

For more docs, see https://docs.github.com/en/communities/using-templates-to-encourage-useful-issues-and-pull-requests/syntax-for-issue-forms

If we do this, we need to ensure that we never disable the "blank issue" option to ensure there's an appropriate safety valve.

Inspect the repository's .github/ISSUE_TEMPLATE directory and compare it with the cargo repository's underlying issue templates. Read GitHub's issue-form syntax documentation first, then define the bug and feature forms while preserving the blank issue option; done means the templates render with structured fields and blank issues remain available.

Written by the indexing model from the issue text.