Moved some config over to an actual config file, improved error handling

src/config.rs

@@ -0,0 +1,29 @@
+use std::{fs, error::Error};
+
+use log::debug;
+use serde::Deserialize;
+
+#[derive(Debug, Deserialize)]
+pub struct Config {
+    pub mqtt: MQTT,
+}
+
+#[derive(Debug, Deserialize)]
+pub struct MQTT {
+    pub host: String,
+    pub port: u16,
+    pub username: String,
+    pub password: Option<String>,
+}
+
+impl Config {
+    pub fn build(filename: &str) -> Result<Self, Box<dyn Error>> {
+        debug!("Loading config: {filename}");
+        let file = fs::read_to_string(filename)?;
+        let mut config: Self = toml::from_str(&file)?;
+
+        config.mqtt.password = Some(std::env::var("MQTT_PASSWORD").or(config.mqtt.password.ok_or("MQTT password needs to be set in either config or the environment!"))?);
+
+        Ok(config)
+    }
+}