feat: 512 CheckboxGroup

[cade-exygy]

Issue Overview

This PR addresses: https://app.zenhub.com/workspaces/bloom-5dc32d7144bd400001315dac/issues/gh/metrotranscom/doorway/512

Description

Adds a CheckboxGroup component to seeds. This component is a group of checkbox inputs. Currently, each of these inputs are styled using the Button.scss classes.

How Can This Be Tested/Reviewed?

• Run storybook
• Go to CheckboxGroup
• Compare to desired Doorway designs linked in ticket
• Ensure tests run successfully

Checklist:

• [x] I have added QA notes to the issue with applicable URLs
• [x] I have performed a self-review of my own code
• [x] I have reviewed the changes in a desktop view
• [ ] I have reviewed the changes in a mobile view
• [x] I have made corresponding changes to the documentation
• [x] My changes generate no new warnings
• [x] I have added tests that prove my fix is effective or that my feature works
• [x] I have exported any new components
• [x] 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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