[Housekeeping] Cache node_modules in GitHub Actions to speed up builds

[jakobe]

Short description of housekeeping request
We would like to cache node_modules in our GitHub Actions to speed up the rpm install step.

Alternatives
Waiting and drinking ☕

Additional context
See: https://docs.github.com/en/actions/guides/caching-dependencies-to-speed-up-workflows

Tasks

Kick Off

• Ensure this issue has been Tech refined with @kirbydesign/kirby-guild and is updated with a clear implementation description
  This issue should be in the Ready to do column of the Kirby kan-ban board before starting implementation
• Assign yourself to this issue and move it to the In progress column of the Kirby kan-ban board

Code

• Create Feature Branch from master branch
• Implement/update unit tests
• Create a draft implementation and push to Github
• Ask a member of @kirbydesign/kirby-guild for a WIP review by creating a draft Pull Request

Code Review

• Open a pull request (or mark the existing draft PR as Ready for review) and ask @kirbydesign/kirby-guild for a review
  Remember to add closes #issueno to the description of the PR.
• Once approved, merge feature branch/PR to master

🎉 Celebrate

[MadsBuchmann]

Unassigned myself as a blocked issue I was assigned to on was just unblocked.