fix(MenuHeading): Fix MenuHeading style overrides (#2002)

* Added className prop to MenuHeading to allow for style overrides

* chore: image-snapshot updates (#2003)

Co-authored-by: ElliotTheHuman <ElliotTheHuman@users.noreply.github.com>

* use styled system for style overrides (#2004)

* Fixed lint error in MenuList.story

* Added ColorProps to MenuHeading interface

* chore: image-snapshot updates (#2005)

Co-authored-by: ElliotTheHuman <ElliotTheHuman@users.noreply.github.com>

Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: Daniel Christopher <dbchristopher@gmail.com>

Author: 3 people