[Notifications]: enhance docs for notification widths

[aagonzales]

We are going to remove the max-width in code for notification as it is too restrictive. However, we still want to make sure notifications are designed at appropriate widths for the content inside it and its relationship to the content around it.

• Explore different context notifications that appear in
• Write new guidelines around how to design for width and setting max-widths on the product side (if needed).

See slack thread for context.

[laurenmrice]

• Check-in with TJ to see if this change is now in code.