feat: new background work process

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

db/migrate/20240213165450_create_worker_roles.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+class CreateWorkerRoles < ActiveRecord::Migration[6.1]
+
+  def change
+    create_table :worker_roles do |t|
+      t.string :role
+      t.string :worker
+      t.datetime :acquired_at
+      t.index :role, unique: true
+    end
+  end
+
+end

db/migrate/20240213171830_create_scheduled_tasks.rb

@@ -0,0 +1,13 @@
+# frozen_string_literal: true
+
+class CreateScheduledTasks < ActiveRecord::Migration[6.1]
+
+  def change
+    create_table :scheduled_tasks do |t|
+      t.string :name
+      t.datetime :next_run_after
+      t.index :name, unique: true
+    end
+  end
+
+end

db/migrate/20240214132253_add_lock_fields_to_webhook_requests.rb

@@ -0,0 +1,12 @@
+# frozen_string_literal: true
+
+class AddLockFieldsToWebhookRequests < ActiveRecord::Migration[6.1]
+
+  def change
+    add_column :webhook_requests, :locked_by, :string
+    add_column :webhook_requests, :locked_at, :datetime
+
+    add_index :webhook_requests, :locked_by
+  end
+
+end