add role and aria attributes to Stepper component

[justinezahiri]

For accessibility considerations, it would be nice to add role (for example role="progressbar') and aria attributes (aria-valuenow, aria-valuemin, aria-valuemax) to the Stepper component props.

Should be useful to add choice of tag for RFS-StepButton (for example <p>) for informative only steppers that are not used as buttons.

I can submit a pull request for that, so let me know.