config: modernize & standardize

[msimerson]

• [x] populate [files] in package.json. Delete .npmignore.
• [x] automated code linting. #3308
  • dep: eslint-plugin-haraka -> @haraka/eslint-config
  • update 'lint' script in package.json
  • verify 'lint' CI test config
• [x] lint: remove duplicate / stale rules from .eslintrc
• [x] automated code formatting (see also #3308)
• [x] automated CI testing.
  • mostly done, verify that local copy of ci.yml is up-to-date.
• [x] CONTRIBUTORS: see 3309
• [x] consistent naming of "special" files like CHANGELOG.md.
• [x] CHANGELOG: verify links at bottom (due to inconsistent tag naming)
  • latest .release does this, fixes most, and warns of errors it can't fix
• [x] verify GitHub repo About link points to npm package
• [x] convert test suites to mocha "style"
  • works great today and with node --test in v18+