Make creating snapshots during update toggleable

[NeevTheDeev]

Some of us don't have a reliable internet connection, updating(downloading) packages could fail many many times and because of that, many(essentially useless) snapshots will be created.
Here is two suggestions I have for fixing this issue :
1- Make system snapshots toggleable during updates. This way the user can manually create one and turn off the automatic one so there will be no additional(and unneeded) snapshots. Another way is that the user can make only one automatic snapshot during the initial update try.
2- only make a snapshot AFTER the packages are downloaded but not installed/upgraded yet. this way if the downloads fail no snapshots will be created and since we are not actually changing anything yet, a snapshot doesn't seems necessary.