Improve experience when reaching URL of offline version
Description
Currently, users are redirected to the archives page when they reach an offline version of the docs.
This MR improves the user experience when reaching an offline version by keeping them on the same URL and displaying an error message on the page.
Preview
Default 404 error:
Error for offline versions:
Closes #635 (closed)
Edited by 🤖 GitLab Bot 🤖