[Notification] add guidance of not supporting or recommending list styles in notifications

[laurenmrice]

Acceptance criteria

We have gotten feedback in support that people have been using line breaks and list styles, like ordered and unordered lists, inside of inline notifications and toast notifications. Figma and React apparently let you customize it to add this, even though it is not actually supported in the code.

Task

• Add guidance to our website documentation, maybe in the Content section under "Body copy", explaining why this is not supported and why we do not recommend using line breaks or list styles inside of notifications to help avoid this confusion.
  • Note: This would also probably be helpful to have dev add this to their documentation, reach out to a dev to discuss.