feat: Updating Next JS to a newer version

[krlz16]

Updating Nextjs

Next has been updated to be able to use its latest features and protect the routes and its server.

• The API_URL was removed since it is not necessary to access the server through it. Instead, we use 'server actions'
• Files were moved inside the src folder.
• In the middleware file the route is protected so that no other route can be accessed, only the main route '/'
• The functionality remains the same, nothing has changed in its logic.
• All test-related files have been removed, they have not been tested at any time and tests need to be added in a next iteration.

[ivegabr]

ok