17492 Update link color for more accessible contrast

What does this MR do?

Improves contrast of links to pass accessibility contrast checker http://webaim.org/resources/contrastchecker/

Screenshots (if relevant)

Before: After:

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 #17492 (closed)

Enabled an automatic merge when the build for bab98d29 succeeds

Status changed to merged

Mentioned in commit 107e8e41

Milestone changed to %8.14

Mentioned in merge request gitlab-com/www-gitlab-com!3851 (merged)