Add utility classes for billing plan page

.gl-bg-purple-500 {
  background-color: $purple-500;
}

.gl-border-purple-500 {
  border-color: $purple-500;
}

.gl-border-purple-500\! {
  border-color: $purple-500 !important;
}

.gl-text-purple-500 {
  color: $purple-500;
}

Plan

• Add to gitlab-ui
• Remove from gitlab