Draft: Experiment: Themed components

What does this MR do and why?

This MR explores themed components via an accent color.

Impacted components:

• GlTabs
• GlCheckbox
• GlRadio
• GlToggle

Related to !201755 (merged), gitlab-org/gitlab-services/design.gitlab.com!5028 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #548836 (closed)