Offer alternative of MySQl 5.7 module if the host cannot update to MySQL 8

Works fine in manual testing :) We don't have automated tests for DB requirements, that would be too heavy to cover.

Added module exists check too and tested that manually as well. Now if the module is already installed, it will be a warning, but if not, it will still be an error, making sure it is installed on Drupal 10.

Automatically closed - issue fixed for 2 weeks with no activity.