[Feature]: Rustserver shutdown-warning in in-game chat

### User story

As a player on a Rust server, I want to receive occasional warnings in the in-game chat before the server shuts down or restarts, so that I have a chance to prepare.

### Game

Rust

### Linux distro

_No response_

### Command

command: stop

### Further information

Hi there

When a Rust server is stopped, which can for example happen with the commands
- `./rustserver stop`
- `./rustserver restart`
- `./rustserver (force-)update`
- `./rustserver backup`

then it will send `Ctrl+c` to the tmux session. This shuts the server down immediately. I have two issues with this:

1. Because this `Ctrl+c` does not explicitly execute a save, any progress of up to 300 seconds will be lost, depending on when the last save happened. (I am not 100 % sure on that, so please correct me if I am wrong.)
2. When there are players connected to the server, they will be surprised by the shutdown and do hot have any chance to prepare.

To fix these, I would like to implement a new method to stop a Rust server, that sends the `quit` command via rcon to the Rust server after 15 minutes. During these 15 minutes, occasional warnings should be sent to the in-game chat, to warn any connected players, so that they can prepare. The `quit` command also ensures that the game is saved directly before the shutdown, so no progress is lost.

Please let me know what you think and have a great day! :)

Kind regards
JuliusZet