Add ClustersHelper with ee cluster button logic

ee/app/helpers/clusters_helper.rb

+module ClustersHelper
+  def enable_add_cluster_button?(project)
+    return true if project.clusters.empty?
+
+    project.feature_available?(:multiple_clusters)
+  end
+end

spec/ee/spec/helpers/clusters_helper_spec.rb

+require 'spec_helper'
+
+describe ClustersHelper do
+  include ApplicationHelper
+
+  describe '.enable_add_cluster_button?' do
+    set(:project) { create(:project) }
+    set(:user) { create(:user) }
+    subject { helper.enable_add_cluster_button?(project) }
+
+    context 'when project does not have a cluster' do
+      it { is_expected.to eq(true) }
+    end
+
+    context 'when project has a cluster' do
+      before do
+        params =
+        {
+          name: 'test-cluster',
+          provider_type: :gcp,
+          provider_gcp_attributes: {
+            gcp_project_id: 'gcp-project',
+            zone: 'us-central1-a',
+            num_nodes: 1,
+            machine_type: 'machine_type-a'
+          }
+        }
+        Clusters::Cluster.create(params.merge(user: user, projects: [project]))
+      end
+
+      context 'when project has multiple clusters available' do
+        before do
+          allow(project).to receive(:feature_available?).with(:multiple_clusters).and_return(true)
+        end
+
+        it { is_expected.to eq(true) }
+      end
+
+      context 'when project does not have multiple clusters available' do
+        before do
+          allow(project).to receive(:feature_available?).with(:multiple_clusters).and_return(false)
+        end
+
+        it { is_expected.to eq(false) }
+      end
+    end
+  end
+end