Extract EE specific files/lines for Release app/serializers

We have the following files containing EE specific code. We should move them to ee/

app/serializers/environment_entity.rb

diff --git a/app/serializers/environment_entity.rb b/home/yorickpeterse/Projects/gitlab/gdk-ee/gitlab/app/serializers/environment_entity.rb
index 4a7d13915dd..f2bceb4d5bf 100644
--- a/app/serializers/environment_entity.rb
+++ b/home/yorickpeterse/Projects/gitlab/gdk-ee/gitlab/app/serializers/environment_entity.rb
@@ -2,6 +2,7 @@
 
 class EnvironmentEntity < Grape::Entity
   include RequestAwareEntity
+  prepend ::EE::EnvironmentEntity # rubocop: disable Cop/InjectEnterpriseEditionModule
 
   expose :id
   expose :name
@@ -10,8 +11,9 @@ class EnvironmentEntity < Grape::Entity
   expose :environment_type
   expose :last_deployment, using: DeploymentEntity
   expose :stop_action_available?, as: :has_stop_action
+  expose :rollout_status, if: -> (*) { can_read_deploy_board? }, using: RolloutStatusEntity
 
-  expose :metrics_path, if: -> (environment, _) { environment.has_metrics? } do |environment|
+  expose :metrics_path, if: -> (*) { environment.has_metrics? } do |environment|
     metrics_project_environment_path(environment.project, environment)
   end
 
@@ -49,6 +51,10 @@ class EnvironmentEntity < Grape::Entity
     request.current_user
   end
 
+  def can_read_deploy_board?
+    can?(current_user, :read_deploy_board, environment.project)
+  end
+
   def can_access_terminal?
     can?(request.current_user, :create_environment_terminal, environment)
   end