Use optionally_search for group labels index page

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/controllers/groups/labels_controller.rb

@@ -11,8 +11,8 @@ class Groups::LabelsController < Groups::ApplicationController
     respond_to do |format|
       format.html do
         @labels = @group.labels
-        @labels = @labels.search(params[:search]) if params[:search].present?
-        @labels = @labels.page(params[:page])
+          .optionally_search(params[:search])
+          .page(params[:page])
       end
       format.json do
         render json: LabelSerializer.new.represent_appearance(available_labels)

app/models/label.rb

@@ -5,6 +5,7 @@ class Label < ActiveRecord::Base
   include Referable
   include Subscribable
   include Gitlab::SQL::Pattern
+  include OptionallySearch
 
   # Represents a "No Label" state used for filtering Issues and Merge
   # Requests that have no label assigned.