Replace append-right-15 css class
What does this MR do?
This removes the .append-right-15 css class and replaces its usage for GitLab UI, gl-mr-5 utility class
This is due to the rem values of gl-mr-5, 2 * 8px = 16px
Since this rule does not comply with our design system guidelines, I "ceiled" the measurement to the closest one that did comply