Add option to never delete logs

aaron.ferris → made their first commit to this issue’s fork.

There is an option in the dropdown for - None -, we could reuse this and check for an not null value in the cleanup method.

Raised an MR.

Thanks, will have a look!

Seems to work!

This is how I tested:

1) Set the retention period to 'Indefinitely'
2) drush core-cron
3) Logs still there
4) Set the period to 'None'
5) drush core-cron
6) Logs gone