Add dashboard notification for users who abandoned express setup.

[JakePT]

Summary

Related issue(s):

• Resolves Add dashboard notification for users who abandoned express setup #13009

Relevant technical choices

I observed that the copy in the notification was specific to the newsletter CTA, so I structured things so that there was a base notice component that handled presentation and navigating to the setup URL, and another component specific to the newsletter CTA that owned the copy and passed the slug to the base component. The idea being that each CTA could have its own notification registered with its own component if necessary. I added a a helper function for checking notification requirements by checking whether a specific CTA type has been abandoned to help with this.

PR Author Checklist

• My code is tested and passes existing unit tests.
• My code has an appropriate set of unit tests which all pass.
• My code is backward-compatible with WordPress 5.2 and PHP 7.4.
• My code follows the WordPress coding standards.
• My code has proper inline documentation.
• I have added a QA Brief on the issue linked above.
• I have signed the Contributor License Agreement (see https://cla.developers.google.com/).

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Code Reviewer Checklist

• Run the code.
• Ensure the acceptance criteria are satisfied.
• Reassess the implementation with the IB.
• Ensure no unrelated changes are included.
• Ensure CI checks pass.
• Check Storybook where applicable.
• Ensure there is a QA Brief.
• Ensure there are no unexpected significant changes to file sizes.

Merge Reviewer Checklist

• Ensure the PR has the correct target branch.
• Double-check that the PR is okay to be merged.
• Ensure the corresponding issue has a ZenHub release assigned.
• Add a changelog message to the issue.

[github-actions]

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