Update security update defaults

[dometto]

@jelletreep SURF has enabled automatic updates by default, so I've 1) turned off the feature in the UU Provisioning component that enabled them, and 2) updates these docs. Could you have a look to see if the current formulations make sense?

I've opted to keep the manual on security updates for now, because it explains the difference between updates for packages in apt and other applications, and because you never know if it it might be necessary again in the future. But I could also rework it so that we only keep the information on different kinds of updates and remove the instructions for enabling automatic OS updates.

[jelletreep]

@dometto , looks good, the formulations make sense and would not do it differently :smile:

[dometto]

Thank you! 🎉