Patterns and Extensions: Update Page component to include variants for patterns/extensions

[kaylachumley]

We need to add a variant or component swap property for extensions and patterns.

• add extensions demo variants to the DIY page content area within the page component

Components/Patterns/Extensions that need added:

• Dashboard
• Catalog View
• Card View
• Primary details

Pro: Allows us to make a component swap directly in the body. rather than turning the UI shell on and off via a boolean.

What we know: The users already have pg headers and page UI shells set up. The goal is to be able to drop the correct content(extensions or pattern) in the page area.

design note: set the padding in the page content area if need be.

Related design issue

[kaylachumley]

reviewed by lucia! making a few more design changes before closing this out @andrew-ronaldson

[kaylachumley]

Closing this out! Everything has been merged to the main component library. We will be revisiting the page component later after some thought on overall architecture. @andrew-ronaldson