Add save and shutdown functions

[Dashboy1998]

Context

• We repeat save and shutdown commands in multiple scripts

Choices

• If Palworld ever adds a better method to save or shutdown this makes it easier to implement.
• Since Use DoExit instead of Shutdown #395 intends to add a feature to change the shutdown command from shutdown 1 to DoExit this means changing it in one place.

Test instructions

1. Test the server still works
2. Verify stopping works
3. Verify updating works
4. Verify backing up works
5. Verify auto_reboot works

Checklist before requesting a review

• I have performed a self-review of my code
• I've added documentation about this change to the README.
• I've not introduced breaking changes.