Hide Cloud Run on GKE behind a feature flag

Currently creating a cluster using Cloud Run on
GKE results in a cluster that serverless
functions cannot be deployed to due to the issue
described in:
https://gitlab.com/gitlab-org/gitlabktl/issues/54

This hides the feature behind a feature flag until
that issue can be addressed in either gitlabktl or
upstream in the tm cli.

app/models/clusters/instance.rb

@@ -9,5 +9,9 @@ module Clusters
     def feature_available?(feature)
       ::Feature.enabled?(feature, default_enabled: true)
     end
+
+    def flipper_id
+      self.class.to_s
+    end
   end
 end

app/views/clusters/clusters/gcp/_form.html.haml

@@ -64,6 +64,7 @@
       %p.form-text.text-muted
         = s_('ClusterIntegration|Learn more about %{help_link_start_machine_type}machine types%{help_link_end} and %{help_link_start_pricing}pricing%{help_link_end}.').html_safe % { help_link_start_machine_type: help_link_start % { url: machine_type_link_url }, help_link_start_pricing: help_link_start % { url: pricing_link_url }, help_link_end: help_link_end }
 
+    - if Feature.enabled?(:create_cloud_run_clusters, clusterable)
       .form-group
         = provider_gcp_field.check_box :cloud_run, { label: s_('ClusterIntegration|Enable Cloud Run on GKE (beta)'),
           label_class: 'label-bold' }

spec/views/projects/clusters/clusters/gcp/_form.html.haml_spec.rb

+# frozen_string_literal: true
+
+require 'spec_helper'
+
+describe 'clusters/clusters/gcp/_form' do
+  let(:admin) { create(:admin) }
+  let(:environment) { create(:environment) }
+  let(:gcp_cluster) { create(:cluster, :provided_by_gcp) }
+  let(:clusterable) { ClusterablePresenter.fabricate(environment.project, current_user: admin) }
+
+  before do
+    assign(:environment, environment)
+    assign(:gcp_cluster, gcp_cluster)
+    allow(view).to receive(:clusterable).and_return(clusterable)
+    allow(view).to receive(:url_for).and_return('#')
+    allow(view).to receive(:token_in_session).and_return('')
+  end
+
+  context 'with all feature flags enabled' do
+    it 'has a cloud run checkbox' do
+      render
+
+      expect(rendered).to have_selector("input[id='cluster_provider_gcp_attributes_cloud_run']")
+    end
+  end
+
+  context 'with cloud run feature flag disabled' do
+    before do
+      stub_feature_flags(create_cloud_run_clusters: false)
+    end
+
+    it 'does not have a cloud run checkbox' do
+      render
+
+      expect(rendered).not_to have_selector("input[id='cluster_provider_gcp_attributes_cloud_run']")
+    end
+  end
+end