chore(.gitlab): add issue templates

Leans in on

• https://docs.gitlab.com/ee/user/project/description_templates.html

Takes inspiration from

• https://gist.github.com/almereyda/d70203ebdf55a82f0a601e58de6b69bc
• https://gitlab.com/gitlab-org/gitlab/-/tree/master/.gitlab/issue_templates
• https://github.com/stevemao/github-issue-templates