[Subtle content switcher] Website docs

[laurenmrice]

Acceptance criteria

• Update the website docs to add the subtle content switcher guidance.

Usage tab

• Add a H3 section with content and and image to Modifiers.

Style tab

• Add content and images.

Color token table page

• Add the new tokens to the color token table.

[github-actions]

Thank you for submitting a feature request. Your proposal is open and will soon be triaged by the Carbon team.

If your proposal is accepted and the Carbon team has bandwidth they will take on the issue, or else request you or other volunteers from the community to work on this issue.

[dianasanborn]

Hey! Just carrying over some small design doc enhancements I captured from the Sustainability Software PAL icon content switcher vs the Carbon one.

We had this do/don't example for the icon content switcher container sizing.