Migration to allow nesting batches

Author: jpcamara

app/models/solid_queue/job_batch.rb

@@ -3,6 +3,7 @@
 module SolidQueue
   class JobBatch < Record
     belongs_to :job, foreign_key: :job_id, optional: true
+    belongs_to :parent_job_batch, foreign_key: :parent_job_batch_id, class_name: "SolidQueue::JobBatch", optional: true
     has_many :jobs, foreign_key: :batch_id
 
     serialize :on_finish_active_job, coder: JSON

db/migrate/20240131013203_create_solid_queue_batch_table.rb

@@ -1,6 +1,7 @@
 class CreateSolidQueueBatchTable < ActiveRecord::Migration[7.1]
   def change
     create_table :solid_queue_job_batches do |t|
+      t.references :parent_job_batch, index: true # FIXME: foreign key
       t.text :on_finish_active_job
       t.text :on_success_active_job
       t.text :on_failure_active_job