feature trio pattern example

[JoshBowdenConcepts]

Summary

Creating a FeatureTrio example within the kitchen sink on Storybook. This example should show users how they can create a FeatureTrio using our components with ease.

List of notable changes:

• added example of FeatureTrio within the kitchen sink

What should reviewers focus on?

• The CSS needed to create this example and the best approach for the components that it uses.
• Understanding the difficulties with each part of the FeatureTrio and what could be improved.

Steps to test:

1. Open storybook in CI-deployed preview environment
2. Go to KitchenSink story in Storybook
3. Verify that the Feature Trio component behaves as described

Supporting resources (related issues, external links, etc):

• https://github.com/github/primer/issues/1548

Contributor checklist:

• [ ] All new and existing CI checks pass
• [ ] Tests prove that the feature works and covers both happy and unhappy paths
• [ ] Any drop in coverage, breaking changes or regressions have been documented above
• [ ] New visual snapshots have been generated / updated for any UI changes
• [ ] All developer debugging and non-functional logging has been removed
• [ ] Related issues have been referenced in the PR description

Reviewer checklist:

• [ ] Check that pull request and proposed changes adhere to our contribution guidelines and code of conduct
• [ ] Check that tests prove the feature works and covers both happy and unhappy paths
• [ ] Check that there aren't other open Pull Requests for the same update/change

Screenshots: