feat: navigation nextjs example

[ltsNotMike]

Test Plan

Follow Readme instructions to set up the project.

• The frontend should display the 3 different pages
• It should be possible to navigate between different pages using the navbar
• Nested items should be displayed accordingly in the navbar
• It should be possible to add both external and internal items to the main navbar without breaking it
• The footer should display all items from Footer Navigation
• Strapi admin panel should work as described in strapi-plugin-navigation documentation

[AndrzejBugdol]

Nested elements are not showing in the app
External items crashes after executing - same error as in PathPage

[ltsNotMike]

Reworks after review done.