Add fault tolerance to update scripts

[MilesBHuff]

At present, the update scripts operate directly on their target locations, meaning that if something goes wrong, the server is broken until manual intervention.
This is not ideal. The update scripts should be modified to run in a temporary location, and then only after a test for validity should they be moved to their target locations.

[MilesBHuff]

The repo-updating script is just git pull, which is fault-tolerant; so it's already being run nightly.

Not having the paper-updating script hasn't been a serious issue on 1.17.1, because there haven't been any updates available for that version in a very long time. The same is true of 1.18.2 and 1.19.4. But eventually we will catch back up to being near to the current version of Minecraft; and at this point, having reliable automatic updates will be pretty important.

It's risky to not have the JVM-updating script run on a regular basis, because Oracle occasionally pushes security fixes and such. The immediate benefit of this ticket is the newfound assurance that our version of Java is up-to-date.