Enhancement/6244 KM Widget Tile New Visitors

[jimmymadon]

Summary

Addresses issue:

• Create the "New visitors" key metric widget tile #6244

Relevant technical choices

• Instead of having a single reusable Metric tile component for all widget tiles, it would be better to have three separate components for the three design types of Key Metric widget tiles. These could be: MetricTileNumeric, MetricTileText and MetricTileTable. I have implemented the first one here and the rest can be implemented when designing the first of those widgets.

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 5.6.
• 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.

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]

Build files for 529891c have been deleted.

[eugene-manuilov]

Thanks, @jimmymadon. This is a good start and almost everything looks okay to me. Found a few things that we need to improve before merging. Please, take a look.

[eugene-manuilov]

Thanks, @jimmymadon. This PR almost looks good to me. Just added two more tiny comments. Please, take a look.

[eugene-manuilov]

Great job, @jimmymadon. Approved.