Studio: Add Sync screen for when there are no sites connected

[katinthehatsite]

Related to https://github.com/Automattic/dotcom-forge/issues/9353

Proposed Changes

This PR adds the UI for the case when where are no connected sites under the Sync tab. it does not implement any functionality for Connect site and Create a site buttons (e.g. clicking the buttons does not do anything). This is only the implementation of the UI part.

Testing Instructions

• Pull the changes from this branch
• Start the app with STUDIO_SITE_SYNC=true npm start
• Navigate to the Sync tab
• Observe the screen that is indicated below:

• Log out of your account
• Observe that the screen is now changed to:

• Log back into your account
• Disable your WiFi or internet connection
• Observe that the screen changes to the following:

• Confirm that the buttons are disabled and that when you hover over them, you can see the tooltip explaining that you need an internet connection.

Figma: RToz6tIuQ7nlZrikBte4GU-fi-4491_115759

Pre-merge Checklist

• [ ] Have you checked for TypeScript, React or other console errors?