Remove append-right-4 CSS class

What does this MR do?

This removes the .append-right-4 css class and replaces its usage for the gl-mr-2 utility class from GitLab-UI

This is due to the rem values of gl-mr-2, 0.5 * 8px = 4px

#217418

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• [-] Separation of EE specific content