Get started page UX improvements: add features card

[ianlin]

Changes proposed in this Pull Request:

Part of #1392, this PR adds the benefits card to the new get started page.

Design for desktop: eQ9O4m2flzrcAiDMXkOW0m-fi-7350%3A121114
Design for mobile: eQ9O4m2flzrcAiDMXkOW0m-fi-7476%3A122839

Screenshots:

Desktop

Mobile

Detailed test instructions:

1. Go to GLA's get started page: https://domain.test/wp-admin/admin.php?page=wc-admin&path=%2Fgoogle%2Fstart
2. Check the third card of the get started page, the UI should align with the design.

Testing for Tracking Events

1. Open your console and run localStorage.setItem('debug', 'wc-admin*').
2. Enable verbose mode in dev tool's console.
3. Go to GLA's get started page: https://domain.test/wp-admin/admin.php?page=wc-admin&path=%2Fgoogle%2Fstart
4. Click on the first Learn More, it should open a new tab to https://woocommerce.com/document/google-listings-and-ads/#google-smart-shopping-campaigns. From the dev console you should see an event is sent with link_id = get-started-features-free-listing-learn-more.
5. Click on the second Learn More, it should open a new tab to https://woocommerce.com/document/google-listings-and-ads/#google-smart-shopping-campaigns. From the dev console you should see an event is sent with link_id = get-started-features-google-ads-learn-more.
6. Click on the third Learn More, it should open a new tab to https://woocommerce.com/document/google-listings-and-ads/#getting-started-with-campaign-analytics. From the dev console you should see an event is sent with link_id = get-started-features-dashboard-learn-more.

Changelog entry

Update - Add the features card for UX improvements on get started page.

[ianlin]

Thanks for the review @eason9487, the PR is ready for the next round of the review.

[eason9487]

Thanks for the changes! Tested locally, and it works as expected. LGTM.