Create secondary colors for buttons with SCSS functions [Proper]

What does this MR do?

• Removes the hardcoded values for button colors and generates them using the darken function
• Adds a border color for outline buttons on hover, focus and active states
• Adds darker colors for outline buttons in their active state

Are there points in the code the reviewer needs to double check?

Naming for new factor variables might not be good enough.

Why was this MR needed?

Increases visibility of alternate states as specified in #24145 (closed)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #24145 (closed)