enable manual configuration property for all test prometheus services

spec/factories/projects.rb

@@ -243,7 +243,8 @@ FactoryBot.define do
       project.create_prometheus_service(
         active: true,
         properties: {
-          api_url: 'https://prometheus.example.com'
+          api_url: 'https://prometheus.example.com',
+          manual_configuration: true
         }
       )
     end