NPM package: Allow router.config to be used in extended router services

[tkohr]

Description

This PR should allow reusing the router.config within a router service extended from the RouterService making it protected and should add the router.config to the exports for the npm package.

Quality Assurance Checklist

• Commit history is devoid of any merge commits and readable to facilitate reviews
• If new logic ⚙️ is introduced: unit tests were added
• If new user stories 🤏 are introduced: E2E tests were added
• If new UI components 🕹️ are introduced: corresponding stories in Storybook were created
• If breaking changes 🪚 are introduced: add the breaking change label
• If bugs 🐞 are fixed: add the backport <release branch> label
• The documentation website 📚 has received the love it deserves

[github-actions]

Affected libs: feature-router,
Affected apps: metadata-editor, datahub, demo,

• 🚀 Build and deploy storybook and demo on GitHub Pages
• 📦 Build and push affected docker images

[coveralls]

coverage: 86.602% (+4.1%) from 82.511%
when pulling cc178f7 on npm-router-service
into e441b92 on main.

[github-actions]

📷 Screenshots are here!