allow specifying config path via env var

src/config.rs

@@ -31,7 +31,14 @@ fn get_db_uri() -> String {
 }
 
 pub(crate) async fn read_config() -> Config {
-    let file = File::open("config.json").expect("failed to read config.json");
+    let filename = match std::env::var("CONFIG_PATH") {
+        Ok(value) => value,
+        Err(_) => "config.json".to_string(),
+    };
+
+    log::info!("loading config file from {}", filename);
+
+    let file = File::open(filename).expect("failed to read config file");
     let reader = BufReader::new(file);
 
     // Read the JSON contents of the file as an instance of `User`.