add more explicit documentation for `...attributes`

[MelSumner]

We need to add more examples that clearly define ...attributes and give several examples for use.

• 2-3 examples of position placement and the outcomes
• understanding how the class attribute is different
• how this effects accessibility attributes like aria-describedby and aria-labelledby

[locks]

This seems mostly addressed by https://guides.emberjs.com/release/components/component-arguments-and-html-attributes/. I think we might want to make the class distinction more obvious as a future iteration.

It is also missing accessibility concerns. Would the better place to include them be https://guides.emberjs.com/release/accessibility/components/ ?

[MelSumner]

It was in the docs but I need to check, I think I remember it didn't make it over after Octane. It should go with the rest of the ...attributes guides and not be separate.