Approve additionally

What does this MR do?

Changes the current behavior for approving merge requests by allowing them to be approved with more people even if the merge request itself already has enough approvals.

Screenshots

3 approvals (approved additionally)

The approve additionally button

Requires n approvals

Requires n more approvals with the remove approval button

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?

Closes #4134 (closed)

ee/app/models/concerns/approvable.rb

@@ -125,7 +125,7 @@ def can_approve?(user)
     return false if user == author
     return false unless user.can?(:update_merge_request, self)
 
-    approvers_left.count == 0 && approvals.where(user: user).empty?
+    approvals.where(user: user).empty?
   end
 
   def has_approved?(user)