feat: Add feature flag to disable local ip filtering

[chriskari]

Description

Changes proposed in this pull request:

• Added feature flag to disable local ip filtering
• Removed unused config/config.yaml file, for local development -> adjust defautlConfig
• Added docs about backend's feature flags
• Use vitest for backend's unit test to allow better mocking

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

[dbadura]

As the config.yaml is shared between frontend and backend.
What if user who deployes busola would like to change some of those features?
https://github.com/kyma-project/busola/blob/main/docs/features.md#features-list-for-backend