[Build] Add clamshell/collapser components

[roadlittledawn]

Summary

Add components for collapser / clamshells. These should be kept basic in style/functionality for now. NR1 Help Center is a good example to draw from.

The component should not output <dl><dt></dt><dd></dd></dl> elements and instead use generic elements like <div>.

Acceptance criteria

• [ ] As a content author, I can add collapsers with one or more rows that, when clicked, toggle show/hide content block.

Helpful links

Example of basic styling in NR1 Help Center > search for Dashboards

[jerelmiller]

Done with #98