Add more CI

[nihaals]

• Testing (related: Set up jest+react-testing-library #29)
  • codecov
• Linting
  • At the moment there is ESLint which is added as code scanning alerts, but these aren't public nor are enforced (failing the test)
  • ESLint
  • sort-package-json
• Docker
  • Blocked by having an initial version of NextJS done
  • Possibly blocked by chore: use preconstruct to manage monorepo #37
• Validate package.json and yarn.lock
  • This is probably covered by yarn install, which will definitely be ran somewhere

[with-heart]

Ye, more CI plz! Whatever gets us closer to guaranteeing that pipeline success = release is good to go. test + lint + build at a minimum imo.