Implement batch functionality

[bensheldon]

Connects to discussion in #417; please keep discussion in that issue. This issue is focused on implementation.

batch = GoodJob::Batch.new
batch.callback_class = "MyCallBackJob" # => Results in `MyCallbackJob.perform_later(batch)`
batch.callback_queue_name = "default"
batch.callback_priority = 0
batch.properties = { user: current_user } # additional state that is serialized/deserialized using ActiveJob/GlobalId
batch.add do
  MyJob.perform_later
  YourJob.perform_later
end

more_job = MoreJob.perform_later
batch.add(more_job)

batch.enqueue # jobs may be performed but the callback won't be triggered till `Batch#enqueue` is called

# Or more succinctly
GoodJob::Batch.enqueue(on_finish: "MyCallbackJob", user: current_user) do |batch|
  MyJob.perform_later
  YourJob.perform_later
  MoreJob.perform_later
end

batch.jobs # => All of the GoodJob::Jobs in the batch
batch.enqueued_at # => When the batch is first enqueued
batch.discarded_at # => When the _first_ job is discarded
batch.completed_at # => When all jobs are completed successfully or discarded

# When the _first_ job within the batch is discarded:
#   MyCallbackJob.perform_later(batch)
# When _all_ jobs within the batch are completed successfully or discarded:
#   MyCallbackJob.perform_later(batch)

Work

• Add a callback after an execution performed and unlocked Add an Execution after_perform_unlocked callback #706
• Implement a batch enqueue that can bulk insert multiple jobs at the same time
• ...