Create task to create iid for existing issues/mr

lib/tasks/migrate/migrate_iids.rake

+desc "GITLAB | Build internal ids for issues and merge requests"
+task migrate_iids: :environment do
+  puts 'Issues'.yellow
+  Issue.where(iid: nil).find_each(batch_size: 100) do |issue|
+    begin
+      issue.set_iid
+      if issue.save
+        print '.'
+      else
+        print 'F'
+      end
+    rescue
+      print 'F'
+    end
+  end
+
+  puts 'done'
+  puts 'Merge Requests'.yellow
+  MergeRequest.where(iid: nil).find_each(batch_size: 100) do |mr|
+    begin
+      mr.set_iid
+      if mr.save
+        print '.'
+      else
+        print 'F'
+      end
+    rescue => ex
+      print 'F'
+    end
+  end
+end