feat: implement a What's New prompt

[Abdomash]

This PR closes #529.

Note

Most things in the PR are ready, but we primarily need an actual video/image to showcase the new features.

Implements the What's New popup

This creates a prompt that will show when the user opens the calendar view for the first time after the extension is updated or installed. The figma reference here.

Screenshot

TODO:

• Use a real image/video instead of the placeholder image
• Make changelog button navigate to settings page
• BUG: the dialog shouldn't reopen after opening the changelog
• Correctly fetch extension version from manifest

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This change is 

[DereC4]

Don't we already have this