Rearrange DeploymentPlatform methods

- Change cluster factory to use default_environment
- Add a constant on cluster to declare default environment
- Change find_cluster_platform_kubernetes to search for a specific
  environment on EE, and ignore environment argument on CE
- Override find_cluster_platform_kubernetes and deployment_platform
  methods
- Remove memoization frmo deployment_platform on EE, otherwise when
  searching for a another platform, once the first one is assigned,
environment parameter is completely ignored

app/models/clusters/cluster.rb

@@ -11,6 +11,7 @@ module Clusters
       Applications::Prometheus.application_name => Applications::Prometheus,
       Applications::Runner.application_name => Applications::Runner
     }.freeze
+    DEFAULT_ENVIRONMENT = '*'.freeze
 
     belongs_to :user
 
@@ -52,6 +53,7 @@ module Clusters
 
     scope :enabled, -> { where(enabled: true) }
     scope :disabled, -> { where(enabled: false) }
+    scope :default_environment, -> { where(environment_scope: DEFAULT_ENVIRONMENT) }
 
     def status_name
       if provider

app/models/concerns/deployment_platform.rb

 module DeploymentPlatform
-  # EE would override this and utilize the extra argument
+  # EE would override this and utilize environment argument
   def deployment_platform(environment: nil)
     @deployment_platform ||=
-      find_cluster_platform_kubernetes ||
+      find_cluster_platform_kubernetes(environment: environment) ||
       find_kubernetes_service_integration ||
       build_cluster_and_deployment_platform
   end
 
   private
 
-  def find_cluster_platform_kubernetes
-    clusters.find_by(enabled: true)&.platform_kubernetes
+  # EE would override this and utilize environment argument
+  def find_cluster_platform_kubernetes(environment: nil)
+    clusters.enabled.default_environment
+      .last&.platform_kubernetes
   end
 
   def find_kubernetes_service_integration

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

@@ -4,13 +4,19 @@ module EE
 
     override :deployment_platform
     def deployment_platform(environment: nil)
-      return super unless environment && feature_available?(:multiple_clusters)
+      find_cluster_platform_kubernetes(environment: environment) ||
+        find_kubernetes_service_integration ||
+        build_cluster_and_deployment_platform
+    end
 
-      @deployment_platform = # rubocop:disable Gitlab/ModuleWithInstanceVariables
-        clusters.enabled.on_environment(environment.name)
-          .last&.platform_kubernetes
+    private
+
+    override :find_cluster_platform_kubernetes
+    def find_cluster_platform_kubernetes(environment: nil)
+      return super unless environment && feature_available?(:multiple_clusters)
 
-      super # Wildcard or KubernetesService
+      clusters.enabled.on_environment(environment.name)
+        .last&.platform_kubernetes
     end
   end
 end

spec/factories/clusters/clusters.rb

@@ -2,7 +2,7 @@ FactoryBot.define do
   factory :cluster, class: Clusters::Cluster do
     user
     name 'test-cluster'
-    sequence(:environment_scope) { |n| "production#{n}/*" }
+    environment_scope Clusters::Cluster::DEFAULT_ENVIRONMENT
 
     trait :project do
       before(:create) do |cluster, evaluator|