Boost: Update UI to account for a website that's not publicly available

[dilirity]

Fixes HOG-14

This mostly affects WoA sites marked as "private".

The UI will now mention that the website is not "publicly accessible" instead of being "offline" when it's set to "private".

Here's what an unavailable feature looks like, when the website is not accessible:

Unfortunately, since the endpoint to retrieve Boost's features returns a 403 for WoA sites, we can't know if the website is using the free or premium.

If a website was using "premium", it would revert to "free". The UI would show:

• Cornerstone Pages would list all entries that a user has added, but they can't be edited (as limit for "free" is 1 entry);
• Critical CSS instead of Cloud CSS;
• Image CDN would be disabled, since Jetpack forces it to "off" when the website is "private" and both are synced;
• Image Size Analyzer disappears;

Proposed changes:

• Update the Boost UI to mention that the website is "not publicly accessible" instead of "offline";
• Introduce PHP interface to help differentiate between features that work offline and features that need the website to be publicly accessible;
• Update UI for Cloud CSS, LCP, Image CDN and Image Size Analyzer, to show that they require the website to be online to function properly;
• Update above mentioned features to not initialize their functionality if the website is not publicly available.

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

HOG-14

Does this pull request change what data or activity we track or use?

no

Testing instructions:

• Make sure the website is set to "Public" before starting your tests. To change that, go to Settings -> Reading and change the Site visibility option to Public;
• Use the Jetpack Beta tester to deploy this on a WoA site (Jurassic Ninja should work);
• Setup Boost and make sure everything works as expected (speed scores load, LCP and Image CDN work, etc);
• Now change the Site visibility to Private and go back to the Boost settings page;
• The UI should show the same message as the one from the screenshot at the top (for LCP as well).

[github-actions]

Thank you for your PR!

When contributing to Jetpack, we have a few suggestions that can help us test and review your patch:

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• ✅ Add testing instructions.
  
• ✅ Specify whether this PR includes any changes to data or privacy.
  
• ✅ Add changelog entries to affected projects
  

This comment will be updated as you work on your PR and make changes. If you think that some of those checks are not needed for your PR, please explain why you think so. Thanks for cooperation 🤖

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Boost plugin:

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[jp-launch-control]

Code Coverage Summary

Coverage changed in 3 files.

File	Coverage	Δ%	Δ Uncovered
projects/plugins/boost/app/modules/class-modules-setup.php	0/110 (0.00%)	0.00%	8 💔
projects/plugins/boost/app/assets/src/js/features/module/module.tsx	0/31 (0.00%)	0.00%	3 ❤️‍🩹
projects/plugins/boost/app/admin/class-config.php	43/44 (97.73%)	0.05%	0 💚

1 file is newly checked for coverage.

File	Coverage
projects/plugins/boost/app/contracts/interface-needs-website-to-be-public.php	0/0 (—%) 🤷

Full summary · PHP report · JS report

_{Coverage check overridden by I don't care about code coverage for this PR Use this label to ignore the check for insufficient code coveage. .}