Add support for bulk editing merge requests

- Add new route and controller for group merge requests
- Edit merge request template to render bulk update sidebar
- Update group bulk update tempate to be reusable with merge requests

app/views/groups/merge_requests.html.haml

+- @can_bulk_update = can?(current_user, :admin_issue, @group)
+
 - page_title "Merge Requests"
 
 - if group_merge_requests_count(state: 'all').zero?
@@ -7,8 +9,13 @@
     = render 'shared/issuable/nav', type: :merge_requests
     - if current_user
       .nav-controls
+        - if @can_bulk_update
+          = button_tag _('Edit merge requests'), class: 'btn btn-default append-right-10 js-bulk-update-toggle'
         = render 'shared/new_project_item_select', path: 'merge_requests/new', label: "New merge request", type: :merge_requests, with_feature_enabled: 'merge_requests', with_shared: false, include_projects_in_subgroups: true
 
   = render 'shared/issuable/search_bar', type: :merge_requests
 
+  - if @can_bulk_update
+    = render 'shared/issuable/group_bulk_update_sidebar', type: :merge_requests
+
   = render 'shared/merge_requests'

ee/app/controllers/groups/merge_requests_controller.rb

+# frozen_string_literal: true
+
+class Groups::MergeRequestsController < Groups::ApplicationController
+  include IssuableActions
+
+  before_action :authorize_admin_group!
+  before_action :verify_group_bulk_edit_enabled!, only: [:bulk_update]
+
+  private
+
+  def verify_group_bulk_edit_enabled!
+    render_404 unless @group.feature_available?(:group_bulk_edit)
+  end
+end

ee/app/views/shared/issuable/_group_bulk_update_sidebar.html.haml

+- type = local_assigns.fetch(:type)
+
 %aside.issues-bulk-update.js-right-sidebar.right-sidebar{ "aria-live" => "polite", data: { 'signed-in': current_user.present? } }
   .issuable-sidebar.hidden
-    = form_tag bulk_update_group_issues_path(@group), method: :post, class: "bulk-update" do
+    = form_tag [:bulk_update, @group, type], method: :post, class: "bulk-update" do
       .block.issuable-sidebar-header
         .filter-item.inline.update-issues-btn.float-left
           = button_tag "Update all", class: "btn update-selected-issues btn-info", disabled: true

ee/config/routes/group.rb

@@ -78,6 +78,12 @@ constraints(::Constraints::GroupUrlConstrainer.new) do
       end
     end
 
+    resources :merge_requests, only: [] do
+      collection do
+        post :bulk_update
+      end
+    end
+
     resources :todos, only: [:create]
     resources :boards, only: [:create, :update, :destroy] do
       collection do