chore: update Card spacings and use HeadingGroup in stories

[jaredcwhite]

PR Overview

This PR addresses #35 and #37

Description

The spacing options for Card have been redone to use regular "t-shirt" sizes.

The stories were also updated to use the HeadingGroup component.

How Can This Be Tested/Reviewed?

Storybook examples: https://deploy-preview-38--storybook-ui-seeds.netlify.app/?path=/story/blocks-card--spacings

Checklist:

• [ ] I have added QA notes to the issue with applicable URLs
• [ ] I have performed a self-review of my own code
• [ ] I have reviewed the changes in a desktop view
• [ ] I have reviewed the changes in a mobile view
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [ ] I have exported any new components
• [ ] My commit message(s) and PR title are polished in the conventional commit format, and any breaking changes are indicated in the message and are well-described

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[github-actions[bot]]

:tada: This PR is included in version 1.6.0 :tada:

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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