Left navigation - Unified theming updates (Core) #8014

Follow up to patternfly/patternfly-design#1571
This issues applies the same accent treatment from the docked nav. Specs and examples are outlined in the link below

Notable changes:

• The border radius on nav items will use border-radius/action/plain/default. This will appear as 6px in the default theme and pilled in the unified theme.
• The new accent mark is using global/color/brand/accent/default. Blue in default PF and red in unified theme.
• New RH ui icon for carets. NEW collapsed state for nav items has an upward facing caret and rotates 180° when expanded.

https://www.figma.com/design/qRn3S225WwGHIdgGZX0LTC/Unified-Theme--Design-Tokens--Styles---Specs?m=auto&node-id=13249-3473&t=GbSxS8vdEiwk05wc-1

Jira Issue: PF-3133