Unify deployment_platform interface with CE

Make sure we override the method from CE, too

app/models/concerns/deployment_platform.rb

 module DeploymentPlatform
+  # EE would override this and utilize the extra argument
   def deployment_platform(environment: nil)
     @deployment_platform ||=
       find_cluster_platform_kubernetes ||

app/models/environment.rb

@@ -137,10 +137,6 @@ class Environment < ActiveRecord::Base
     end
   end
 
-  def deployment_platform
-    project.deployment_platform(environment: self)
-  end
-
   def has_terminals?
     deployment_platform.present? && available? && last_deployment.present?
   end
@@ -234,6 +230,10 @@ class Environment < ActiveRecord::Base
     self.environment_type || self.name
   end
 
+  def deployment_platform
+    project.deployment_platform(environment: self)
+  end
+
   private
 
   # Slugifying a name may remove the uniqueness guarantee afforded by it being

ee/app/models/concerns/ee/deployment_platform.rb

 module EE
   module DeploymentPlatform
+    extend ::Gitlab::Utils::Override
+
+    override :deployment_platform
     def deployment_platform(environment: nil)
       return super unless environment && feature_available?(:multiple_clusters)