Hide about and remove "Error" duplicate svelte file

[HasinduLanka]

Summary

Hide the about page, until it's finished.

Details

Add ability to exclude any page from generating using site-settings.js This only works if there's no links to that page from other generated pages.

/about page is excluded in this PR.

Side fix :

There were two error pages (Error, error). Error.svelte is removed.

Checklist

• [x] Tested Changes
• [x] Stakeholder Approval
• [x] No error nor warning in the console.

Test Environments

• Linux
• VSCode