Add IP/PORT options to installer engine

The NixOS module already has options for it, but they are not used at the moment.

```rust
let ip = match env::var("IP") {
Ok(val) => IpAddr::from_str(&val).unwrap(),
Err(_) => IpAddr::V4(Ipv4Addr::from([127, 0, 0, 1])),
};
let port = match env::var("PORT") {
Ok(val) => val,
Err(e) => "3000".to_string(),
};
```