Use the new Members::ApproveAccessRequestService in Member#add_user

Signed-off-by: Rémy Coutable <remy@rymai.me>

app/models/member.rb

@@ -103,7 +103,7 @@ class Member < ActiveRecord::Base
       }
       if member.request?
-        member.accept_request
+        ::Members::ApproveAccessRequestService.new(source, current_user, id: member.id).execute
       else
         member.save
       end