Fix #1342: revert to using Markdown format for issue templates

[mhucka]

GitHub issue forms seemed like a good idea, and the web interface is nice. After using them for some time, though, they turn out to introduce too much friction:

• On the command-line, gh issue create does not handle them – in fact, it doesn't even know they exist! Conversely, Markdown-based issue templates work fine using gh, including when you open an external editor.

• There was a hope that maybe GitHub would add proper support for YAML-based issue templates in gh eventually, but that still has not happened.

• The YAML version of templates is harder and more error-prone to edit and maintain.

This converts the forms back to GitHub's Markdown format for issue templates.

[gemini-code-assist]

Code Review

This pull request transitions the repository's GitHub issue templates from YAML configuration files to Markdown-based templates, introducing new templates for bug reports, feature requests, questions, and tasks. Feedback on the changes points out that in the bug report template, the front matter key for the template description should be about instead of description to ensure it displays correctly in the GitHub issue chooser.

[gemini-code-assist]

Code Review

This pull request updates the GitHub issue templates by replacing the previous YAML-based bug report and feature request forms with Markdown-based templates. It also introduces a new Markdown template for project tasks and updates the issue configuration file (config.yml) to include contact links for GitHub Discussions and OpenFermion documentation. There are no review comments, and I have no feedback to provide.