Add association project -> kubernetes_namespaces

kubernetes_namespaces is not needed for project import/export as it
tracks internal state of kubernetes integration

app/models/project.rb

@@ -238,6 +238,7 @@ class Project < ActiveRecord::Base
   has_one :cluster_project, class_name: 'Clusters::Project'
   has_many :clusters, through: :cluster_project, class_name: 'Clusters::Cluster'
   has_many :cluster_ingresses, through: :clusters, source: :application_ingress, class_name: 'Clusters::Applications::Ingress'
+  has_many :kubernetes_namespaces, class_name: 'Clusters::KubernetesNamespace'
 
   has_many :prometheus_metrics
 

spec/lib/gitlab/import_export/all_models.yml

@@ -304,6 +304,7 @@ project:
 - import_export_upload
 - repository_languages
 - pool_repository
+- kubernetes_namespaces
 award_emoji:
 - awardable
 - user

spec/models/project_spec.rb

@@ -87,6 +87,7 @@ describe Project do
     it { is_expected.to have_many(:pipeline_schedules) }
     it { is_expected.to have_many(:members_and_requesters) }
     it { is_expected.to have_many(:clusters) }
+    it { is_expected.to have_many(:kubernetes_namespaces) }
     it { is_expected.to have_many(:custom_attributes).class_name('ProjectCustomAttribute') }
     it { is_expected.to have_many(:project_badges).class_name('ProjectBadge') }
     it { is_expected.to have_many(:lfs_file_locks) }