chore: Migrate backend to using vitest

[chriskari]

Description

Changes proposed in this pull request:

• Migrate backend to using vitest to allow for better mocking and consistency with frontend
• Added proper unit tests of ip filtering feature flag connected to feat: Add feature flag to disable local ip filtering #4610
• ...

Related issue(s)
#4553

Definition of done

• The PR's title starts with one of the following prefixes:
  • feat: A new feature
  • fix: A bug fix
  • docs: Documentation only changes
  • refactor: A code change that neither fixes a bug nor adds a feature
  • test: Adding tests
  • revert: Revert commit
  • chore: Maintainance changes to the build process or auxiliary tools, libraries, workflows, etc.
• Related issues are linked. To link internal trackers, use the issue IDs like backlog#4567
• Explain clearly why you created the PR and what changes it introduces
• All necessary steps are delivered, for example, tests, documentation, merging