PromotionCodeBatch fails generating million codes

[DanielePalombo]

When a new promotion with 2.5m new promo codes was created, it just generated about 250k promo codes and then stopped.

The PromotionBatch screen this error: Errored: #<ActiveRecord::RecordInvalid: Validation failed: Value has already been taken>
It seems that when the PromotionCode creation fails, it raises an exception that stops the worker.

solidus/core/app/models/spree/promotion_code/batch_builder.rb

Lines 36 to 50 in 152b022

	while created_codes < number_of_codes
	max_codes_to_generate = [batch_size, number_of_codes - created_codes].min
	new_codes = Array.new(max_codes_to_generate) { generate_random_code }.uniq
	codes_for_current_batch = get_unique_codes(new_codes)
	codes_for_current_batch.each do |value|
	Spree::PromotionCode.create!(
	value: value,
	promotion: promotion,
	promotion_code_batch: promotion_code_batch
	)
	end
	created_codes += codes_for_current_batch.size
	end

I would like to propose changing this behavior and rescuing the exception inside the loop, so we can skip the failed code creation and continue to the next one.

Solidus Version:
All solidus version

To Reproduce
Create a promotion with 2.5M code

Current behavior
The Spree::PromotionCode::BatchBuilder worker fails with ActiveRecord::RecordInvalid: Validation failed: Value has already been taken without completing the promotion codes generation.

Expected behavior
The Spree::PromotionCode::BatchBuilder worker generates all the PromotionCodes.