Extract EE specific Cluster code into an EE concern

app/models/clusters/cluster.rb

 module Clusters
   class Cluster < ActiveRecord::Base
+    prepend EE::Clusters::Cluster
+
     include Presentable
-    prepend HasEnvironmentScope
 
     self.table_name = 'clusters'
 
@@ -32,7 +33,6 @@ module Clusters
     accepts_nested_attributes_for :platform_kubernetes, update_only: true
 
     validates :name, cluster_name: true
-    validate :unique_environment_scope
     validate :restrict_modification, on: :update
 
     delegate :status, to: :provider, allow_nil: true
@@ -105,15 +105,6 @@ module Clusters
 
     private
 
-    def unique_environment_scope
-      if project && project.clusters.where(environment_scope: environment_scope).where.not(id: self.id).exists?
-        errors.add(:base, "cannot add duplicated environment scope")
-        return false
-      end
-
-      true
-    end
-
     def restrict_modification
       if provider&.on_creation?
         errors.add(:base, "cannot modify during creation")

ee/app/models/ee/clusters/cluster.rb

+module EE
+  module Clusters
+    module Cluster
+      extend ActiveSupport::Concern
+
+      prepended do
+        prepend HasEnvironmentScope
+
+        validate :unique_environment_scope
+      end
+
+      def unique_environment_scope
+        if project && project.clusters.where(environment_scope: environment_scope).where.not(id: self.id).exists?
+          errors.add(:base, "cannot add duplicated environment scope")
+          return false
+        end
+
+        true
+      end
+    end
+  end
+end