[Button] Accessibility guidelines

[aweell]

Story description

Add accessibility section to the button component documentation:

Widget attributes

• aria-label: use it in cases where a text label is not available in the DOM
• aria-labelledby: use when there is a text labeling is available in the DOM
• aria-describedby: use to indicate the id of the text element that describes the button

References

• Understanding WCAG 2.2 - 2.4.7: Focus Visible
• Understanding WCAG 2.2 - 3.2.2: On Input
• WAI-ARIA Authoring Practices 1.2 -Button Design Pattern

[aweell]

Closed via #633