test: add side navigation integration tests

[petermakowski]

Done

• add jest & @testing-library/dom dependencies and basic setup for integration tests with JSDOM
• Add side navigation tests

Note: includes commits from https://github.com/canonical/vanilla-framework/pull/4536

Check if PR is ready for release

If this PR contains Vanilla SCSS code changes, it should contain the following changes to make sure it's ready for the release:

• [ ] PR should have one of the following labels to automatically categorise it in release notes:
  • Feature 🎁, Breaking Change 💣, Bug 🐛, Documentation 📝, Maintenance 🔨.
• [ ] Vanilla version in package.json should be updated relative to the most recent release, following semver convention:
  • if CSS class names are not changed it can be bugfix relesase (x.x.X)
  • if CSS class names are changed/added/removed it should be minor version (x.X.0)
  • see the wiki for more details
• [ ] Any changes to component class names (new patterns, variants, removed or added features) should be listed on the what's new page.
• [ ] Documentation side navigation should be updated with the relevant labels.

[webteam-app]

Demo starting at https://vanilla-framework-4537.demos.haus

[petermakowski]

We decided to close this for now. We can get much more value from e2e tests: https://github.com/canonical/vanilla-framework/pull/4540