Extract EE specific Clusters::CreateService logic to ee directory

app/services/clusters/create_service.rb

 module Clusters
   class CreateService < BaseService
+    prepend EE::Clusters::CreateService
+
     attr_reader :access_token
 
     def execute(access_token = nil)
@@ -29,9 +31,7 @@ module Clusters
     end
 
     def can_create_cluster?
-      return true if project.clusters.empty?
-
-      project.feature_available?(:multiple_clusters)
+      project.clusters.empty?
     end
   end
 end

ee/app/services/ee/clusters/create_service.rb

+module EE
+  module Clusters
+    module CreateService
+      extend ::Gitlab::Utils::Override
+
+      override :can_create_cluster?
+      def can_create_cluster?
+        super || project.feature_available?(:multiple_clusters)
+      end
+    end
+  end
+end