[dry-operation] Support current transaction for ActiveRecord extension

Ideas
1

This is my first post, so bear with me if I am missing something here.

Recently, I found that I wanted to access the current transaction to a callback after commit; not a model-level but transaction-level itself.

Using ActiveRecord you can do:

ActiveRecord::Base.transaction do |tx|
  # Some logic here

  tx.after_commit do
    # some logic here
  end
end

However, even though we can do transactions with dry-operation using the right extension, it does not allow to access the transaction for such behavior.

class CreateAppointOperation < Dry::Operation
  include Dry::Operation::Extensions::ActiveRecord

  def call
    transaction do |tx|
      service = step find_service
      client = step find_or_create_client

      appointment = step create_appointment(validated_params)

      # Accesing tx is not possible
      # We could probably access through current_transaction from ActiveRecord itself
      # It would just be much cleaner to have it here
      tx.after_commit do
        AppointmentCreatedJob.perform_later(appointment)
      end

      appointment
    end
  end

  # rest of the logic here ..
end

I have a monkey patching right now setup in my project, but I did not wanted to open a PR as the guidelines explicitly mention to avoid doing so without first discussing in the forum:

Rails.configuration.to_prepare do
  require 'dry/operation/extensions/active_record'

  class Dry::Operation::Extensions::ActiveRecord::Builder < Module
    def included(klass)
      default_connection = @connection
      default_options = @options

      define_method(:transaction) do |connection = default_connection, **opts, &steps|
        intercepting_failure do
          result = nil
          # Mind the block argument next line
          connection.transaction(**default_options.merge(opts)) do |tx|
            intercepting_failure(->(failure) {
              result = failure
              raise ::ActiveRecord::Rollback
            }) do
                result = steps.(tx)
              end
          end
          result
        end
      end
    end
  end
end

I am happy to jump in, and submit a PR with this small fix, and tests to cover it, as well as updating the docs.