Update GHA issues

[sjspielman]

Closes #124

This PR updates the automated issues that are filed via GHA, as follows:

• Delete deprecated issues:

  • setup-issue-templates/delete-directories-and-rename.md
  • setup-issue-templates/update-header-pages.md
  • setup-issue-templates/tailor-to-workshop-content.md
  • I was able to deprecate this issue in this PR by adding case/switch to workshop/workshop-logistics.md for a quick string about workshop content, using the new config variable site.workshop_content.

• Update existing issues:

  • setup-issue-templates/update-config.md

• Add new issue:

  • setup-issue-templates/copy-completed-notebooks.md

Note that htmlpreview was already removed from setup-issue-templates/draft-schedule.md & setup-issue-templates/final-schedule.md, so no further changes to those in this PR.

Reviewers, let me know if anything could use more or less detail!

[sjspielman]

Went ahead with inline, why not!

Renders fine, for example for intro-single-cell -