feat: new background work process

This removes all previous dependencies on RabbitMQ and the need to run separate cron and requeueing processes.

spec/factories/queued_message_factory.rb

@@ -0,0 +1,40 @@
+# frozen_string_literal: true
+
+# == Schema Information
+#
+# Table name: queued_messages
+#
+#  id            :integer          not null, primary key
+#  attempts      :integer          default(0)
+#  batch_key     :string(255)
+#  domain        :string(255)
+#  locked_at     :datetime
+#  locked_by     :string(255)
+#  manual        :boolean          default(FALSE)
+#  retry_after   :datetime
+#  created_at    :datetime
+#  updated_at    :datetime
+#  ip_address_id :integer
+#  message_id    :integer
+#  route_id      :integer
+#  server_id     :integer
+#
+# Indexes
+#
+#  index_queued_messages_on_domain      (domain)
+#  index_queued_messages_on_message_id  (message_id)
+#  index_queued_messages_on_server_id   (server_id)
+#
+FactoryBot.define do
+  factory :queued_message do
+    server
+    message_id { 1234 }
+    domain { "example.com" }
+    batch_key { nil }
+
+    trait :locked do
+      locked_by { "worker1" }
+      locked_at { 5.minutes.ago }
+    end
+  end
+end