Remove string concat duplicated logic from services

app/models/clusters/cluster.rb

@@ -37,7 +37,7 @@ module Clusters
 
     has_one :platform_kubernetes, class_name: 'Clusters::Platforms::Kubernetes', inverse_of: :cluster, autosave: true
 
-    def self.has_one_cluster_application(name)
+    def self.has_one_cluster_application(name) # rubocop:disable Naming/PredicateName
       application = APPLICATIONS[name.to_s]
       has_one application.association_name, class_name: application.to_s # rubocop:disable Rails/ReflectionClassName
     end

app/services/clusters/applications/base_service.rb

@@ -77,6 +77,10 @@ module Clusters
         params[:application]
       end
 
+      def application_class
+        Clusters::Cluster::APPLICATIONS[application_name]
+      end
+
       def create_oauth_application(application, request)
         oauth_application_params = {
           name: params[:application],

app/services/clusters/applications/create_service.rb

@@ -10,7 +10,7 @@ module Clusters
       end
 
       def builder
-        cluster.public_send(:"application_#{application_name}") || # rubocop:disable GitlabSecurity/PublicSend
+        cluster.public_send(application_class.association_name) || # rubocop:disable GitlabSecurity/PublicSend
           cluster.public_send(:"build_application_#{application_name}") # rubocop:disable GitlabSecurity/PublicSend
       end
     end

app/services/clusters/applications/destroy_service.rb

@@ -16,7 +16,7 @@ module Clusters
       private
 
       def builder
-        cluster.public_send(:"application_#{application_name}") # rubocop:disable GitlabSecurity/PublicSend
+        cluster.public_send(application_class.association_name) # rubocop:disable GitlabSecurity/PublicSend
       end
     end
   end

app/services/clusters/applications/update_service.rb

@@ -10,7 +10,7 @@ module Clusters
       end
 
       def builder
-        cluster.public_send(:"application_#{application_name}") # rubocop:disable GitlabSecurity/PublicSend
+        cluster.public_send(application_class.association_name) # rubocop:disable GitlabSecurity/PublicSend
       end
     end
   end