Update modal elements for My Jetpack modal interstitial

[grzegorz-cp]

Fixes https://github.com/Automattic/jetpack-roadmap/issues/2125

Proposed changes:

• introduce a new component using product slug to get the correct price
• add a new list component displaying features
• fix layout to stretch content in the left column
• fix component CSS variables for My Jetpack
• remove unused hideCloseButton prop
• prepare the modal component to be used with specific products and update exported file structure

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

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

Testing instructions:

• Checkout this branch locally
• Run storybook with cd projects/js-packages/storybook and pnpm run storybook:dev
• When storybook loads, navigate to My Jetpack and test Product Interstitial Modal

[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WordPress.com Simple site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin, and enable the add/my-jetpack-modal-interstitial-update branch.

• To test on Simple, run the following command on your sandbox:

  bin/jetpack-downloader test jetpack add/my-jetpack-modal-interstitial-update
  

Interested in more tips and information?

• In your local development environment, use the jetpack rsync command to sync your changes to a WoA dev blog.
• Read more about our development workflow here: PCYsg-eg0-p2
• Figure out when your changes will be shipped to customers here: PCYsg-eg5-p2

[github-actions]

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[elliottprogrammer]

The interstitial(s) are lookin really nice @grzegorz-cp! 😃.
The testing instructions didn't state what I should be testing exactly, like the design, or certain specific functionality, or just an overall review of the code & appearance, etc. So I went ahead and just pointed out some small improvements in the code, and also I see some design discrepancies between the Figma design and the interstitial modal, that I have pointed out in the screenshot below:

Other than that, everything is looking really nice! 🙌

[elliottprogrammer]

Hmm, maybe a nitpick, but this prop name is confusing, since it's type is ReactNode, I was expecting this prop would pass in an entire button element or any sort of trigger component, but it turns out that this is just the button "label" (or text). Ideally this would be named triggerButtonLabel or triggerButtonText.

[elliottprogrammer]

I'm not sure if this is an actual WordPress coding standard, but all boolean variables ideally should be prefixed with is, has, can, should, etc. So for example, the boolean props here in this component would ideally be renamed to:
isSecondaryButtonExternal,
isButtonDisabled,
isButtonExternal

[elliottprogrammer]

Nitpick, "full with" is misspelled. It should be "full width".

[elliottprogrammer]

To utilize the benefits if Jetpack Redirects ( PCYsg-pY7-p2 ), this href should be:
href={ getRedirectUrl( 'ai-assistant-fair-usage-policy' ) }