Fix sending duplicate emails

[iGerchak]

Preconditions

1. Magento 2.2.4 or 2.2.5
2. Wyomind Cron Scheduler v1.4.0

Description

We installed Wyomind Cron Scheduler v1.4.0 and in the result, we have duplicates email (5-6 emails for 1 order).
This hotfix warns against similar situations with sending duplicate emails and adds a limit of 50 emails per cronjob.

Steps to reproduce:

1. Disable crontab
2. Make 2 or more orders
3. Enable crontab

Expected result

No duplicate Emails.

Actual result

Duplicate Emails.

[magento-cicd2]

All committers have signed the CLA.

[magento-engcom-team]

Hi @iGerchak. Thank you for your contribution
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[ihor-sviziev]

As we discussed - it's not good idea to clean collection every time. It's better to fix root of the issue - this object should NOT be shared. Please add shared="false" to https://github.com/magento/magento2/blob/2.2-develop/app/code/Magento/Sales/etc/di.xml#L355-L395

[ihor-sviziev]

1. AFAIK current page is set to 1 by default, no need to specify it
2. Could you extract 50 to system configuration, near sales_email/general/async_sending and make it configurable via admin? Please make it configurable globally only (the same as sales_email/general/async_sending)

[ihor-sviziev]

Reopened this PR just to restart Travis builds

[ihor-sviziev]

You're not limiting email sending, you're limiting how many entities (orders/shipments/etc) will be processed per one cron run.
Please Update label and description

[magento-engcom-team]

Hi @ihor-sviziev, thank you for the review.
ENGCOM-2787 has been created to process this Pull Request

[magento-engcom-team]

@iGerchak thank you for contributing. Please accept Community Contributors team invitation here to gain extended permissions for this repository.

[ihor-sviziev]

Build on travis failed. Could you update tests?

[magento-engcom-team]

Hi @iGerchak. Thank you for your contribution.
We will aim to release these changes as part of 2.2.7.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.