Animation - update Motion guidelines

[srambach]

Update the Motion guidelines page with information about the new animation features.

Probably should include:

• Expand/collapse information?
• How to trigger things like notification bell
• Any figma info? That section seems unfinished currently
• How to "turn off" animations for testing or other purposes
• What else?

Motion information is currently located in the Design Foundations section of the site. Should there be a related section in the Developer Resources for some of this information that is much more related to implementation (such as how to trigger a notification bell) or turning off animations for testing.

Sheet with list of changes and opt-ins