Add smoke tests

[xai]

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The tests ensure the following core features:

• Main Page Navigation: Confirming the visibility of extensions on the homepage.
• Scroll Validation: Scrolling to validate the dynamic loading of additional extensions.
• Search Functionality: Testing search inputs and category filters validating the changing results.
• Extension Details: Verifying the presence of specific extension details, including title, tabs, download counts, and version selection.
• Direct Download: Ensuring the successful download of extensions.

A Github workflow has been added to schedule a daily run against the production site at open-vsx.org.