Introduce keyset pagination for Branches API

config/feature_flags/development/branch_list_keyset_pagination.yml

 ---
 name: branch_list_keyset_pagination
 introduced_by_url: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/35819
-rollout_issue_url: 
+rollout_issue_url:
 milestone: '13.2'
 type: development
 group: group::source code
-default_enabled: false
+default_enabled: true

lib/gitlab/pagination/gitaly_keyset_pager.rb

@@ -26,11 +26,11 @@ module Gitlab
       private
 
       def keyset_pagination_enabled?
-        Feature.enabled?(:branch_list_keyset_pagination, project) && params[:pagination] == 'keyset'
+        Feature.enabled?(:branch_list_keyset_pagination, project, default_enabled: true) && params[:pagination] == 'keyset'
       end
 
       def paginate_first_page?
-        Feature.enabled?(:branch_list_keyset_pagination, project) && (params[:page].blank? || params[:page].to_i == 1)
+        Feature.enabled?(:branch_list_keyset_pagination, project, default_enabled: true) && (params[:page].blank? || params[:page].to_i == 1)
       end
 
       def paginate_via_gitaly(finder)