Introducing a dedicated cron.log file for logging cron related info, …

[hostep]

…this reduces output in the system.log file.

Description

Magento 2.2.5 introduced better handling of cron job locking, but also added some extra logging output. This happened in f274f03 (file: app/code/Magento/Cron/Observer/ProcessCronQueueObserver.php).
For example, following extra output is logged now:

• Cron Job sales_send_order_emails is run
• Cron Job sales_send_order_emails is successfully finished. Statistics: {"sum":0.00037288665771484,"count":1,"realmem":0,"emalloc":752,"realmem_start":39845888,"emalloc_start":36019592}
• ...

But all this gets logged in the system.log file, and it happens for every cron job. Some of them run every single minute, so this causes a lot of extra output in the system.log file, which makes it harder to find other non-cron related output in that file.

This PR introduces a new file cron.log where all cron related output gets logged.

Fixed Issues (if relevant)

1. system.log rapidly increasing after Magento CE 2.2.5 update (cron logs) #17190: system.log rapidly increasing after Magento CE 2.2.5 update (cron logs)

Manual testing scenarios

1. Set up a clean Magento
2. Run bin/magento cron:run
3. Expect to see no cron related messages in system.log, but now in a dedicated cron.log file

Contribution checklist

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @hostep. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

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[VladimirZaets]

@magento-engcom-team give me test instance

[magento-engcom-team]

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[magento-engcom-team]

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[magento-engcom-team]

Hi @slavvka, thank you for the review.
ENGCOM-3062 has been created to process this Pull Request

[magento-engcom-team]

Hi @hostep. Thank you for your contribution.
We will aim to release these changes as part of 2.3.1.
Please check the release notes for final confirmation.

[slavvka]

Hi @hostep, we need the fix to be delivered also to 2.2-develop branch so please don't forget to port this PR to 2.2-develop; you can do it easily using the Porting Tool, https://devdocs.magento.com/guides/v2.2/contributor-guide/contributing.html#porting-tool