Display error page in case an unmatched route is hit

[tmscarla]

Description

Currently, pointing to a non-existing page in PCUI returns an empty page, which can be confusing for customers.

This PR introduces a new error page template in PCUI that displays a clear message to the user indicating that an error has occurred, along with options for resolving the issue.

Changelog entry

• Add error page to be displayed if an unmatched route is hit

How Has This Been Tested?

• Manual tests navigating to unmatched routes, even in the case where the frontend is served by the backend

PR Quality Checklist

• [ ] I added tests to new or existing code
• [ ] I removed hardcoded strings and used our i18n solution instead (see here)
• [ ] I made sure no sensitive info gets logged at any time in the codebase (see here) (e.g. no user info or details, no stacktraces, etc.)
• [ ] I checked that infrastructure/update_infrastructure.sh runs without any error
• [x] I checked that npm run build builds without any error
• [x] I checked that clusters are listed correctly
• [ ] I checked that a new cluster can be created (config is produced and dry run passes)
• [ ] I checked that login and logout work as expected

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[mtfranchetto]

@tmscarla issue: have you tried testing the frontend when served from the backend? Serving from the backend as a public folder differs from going to Next.js directly. If you try accessing a non-existing path on Flask at the moment you receive a 404 error, and the index.html is not served.

[mendaomn]

test: let's add an e2e for this case

[tmscarla]

test: let's add an e2e for this case

Consider it done :)

@tmscarla issue: have you tried testing the frontend when served from the backend? Serving from the backend as a public folder differs from going to Next.js directly. If you try accessing a non-existing path on Flask at the moment you receive a 404 error, and the index.html is not served.

Yes I checked following the instructions you provided and I can confirm that it works! 👍🏻