Added shutdown and save functions

[Dashboy1998]

Context

• Added shutdown and save functions which is staging for Implement CLI for RCON commands #401
• Code from Move countdown to function for auto update and auto reboot #392
• Implemented Use DoExit instead of Shutdown #395

Choices

• Switched to DoExit so it's instant
• Using functions so in the future if Palworld changes how to save or shutdown we only need to update the function instead of changing lots of code.

Test instructions

Start the server and verify it saves and shutdowns gracefully.

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.