What's new pattern documentation

[RichKummer]

Follow on #6693

The ‘what’s new pattern’ is a critical experience enhancement to introduce incremental improvements and new feature introductions (NFIs) directly within their product experience. With the design finalized and handed off to development, we need to write additional documentation on the pattern.

WIP:
Design specs
Prototype
Guidance

Tasks

• Update content to reflect What's new UX design updates
• Update What's new images
• Review documentation updates with designers

[ljcarot]

Cool! Does this need refinement? @RichKummer @bndege2