Automated migrations: create job to check source site requirements

Job input

This job will check current requirements on the source site, if checks pass, enqueue the next job in the automated migration sequence.

Plugin incompatibility. The one used by HEs is the one on this Tampermonkey script: pfxNDN-if-p2. If there are incompatible plugins we should add a note to the ZD ticket and return
WP and PHP version. Check for WP 4.0+ and PHP 5.6+. If this conditions aren't met, leave a note on the ZD ticket and return
If WooCommerce is installed, leave a note on the ZD ticket and return
Toggle on the migration-stop-emails sticker on the destination site Blog RC to prevent migration notifications from being sent to the customer.
Enqueue the job to transfer the destination site