repeated (failed) deploys fill disk with backups

[freephile]

Environment

• Machine or Virtual Machine details: (All of VirtualBox, VMWare, Digital Ocean, AWS, etc)
• Operating System: (all)
• meza version hash: 3aee77a

Issue details

Deploys will automatically create backups of all databases which can fill available storage quickly (starting with 36GB databases). To remedy this default behavior, I propose to patch the task so that backup is intentional and explicit.

[jamesmontalvo3]

I'd be okay with a config var that makes it not default to creating backups. Also having a method to keep only the last X backups would be a good idea. I don't think it should default to not backing up. meza deploy runs update.php, and update.php docs clearly say to do a backup before running.

Also note that #1088 adds the capability to periodically cleanup backups. It's far from perfect.