v2.5.6

WPS DOM + SDS clean up and purple color addition

1. Remove <hr> element from Related Stories in WPS and replace with border bottom styling in SDS
2. H4 and h3 headline DOM clean up - correcting font sizing cascade
3. Impact class clean up in DOM - remove extra rules in fixes.css file
4. Update purple/opinion hex value custom property in SDS - add new purple color custom property for opinion related content

Related Jira epic: PE-401