[Bug]: Can't stop Rust server gracefully

### User story

As a rust server owner, I need LGSM to stop the server via a `quit` RCON command to trigger a clean save on exit

### Game

Rust

### Linux distro

Ubuntu 24.04

### Command

command: stop

### Further information

LGSM's default `stopmode` for Rust is CTRL+C, which causes a hard shutdown that tends to have nasty side effects like forgetting teams, because the server doesn't get a chance to generate a full save.

Changing `stopmode` to `quit` results in failure, apparently because LGSM tries to send it to the server console instead of via RCON.

### Relevant log output

```shell
rustserver@ubuntultsvm:~$ ./rustserver stop
[ ERROR ] Stopping rustserver: Graceful: sending "quit": FAIL
[ OK ] Stopping rustserver: LinuxGSM
```
```

### Steps to reproduce

1. Configure server for `stopmode=3`
2. `./rustserver start` and wait for server startup to complete
3. `./rustserver stop`