Define usage guidelines for text styles for emphasis and hyperlinks

We have a few examples of text in about.gitlab.com, customers.gitlab.com, and gitlab.com where you cannot tell if text is clickable unless you hover over it.

It would be helpful to add separate styles and guidelines in Pajamas for text that needs emphasis but isn't a link, and different styles for text links that will help users know what they can click on.

Documentation about when to use different text styles for emphasis and interactivity would improve consistency across the product.

Making it easier to tell what is interactive vs what is text will help with product discoverability.