DEV: Resolve majority of CI issues (PR #123)

(these commits were originally in DEV: Update CI workflows by discoursebot · Pull Request #91 · discourse/discourse-data-explorer · GitHub, but buildbot force-pushed the branch and removed them)

There are still a few remaining template-lint issues which will require some refactoring. But I think we can merge this PR for now as a starting point. Sound ok @CvX ?