installer: tokio runtime flavor current_thread

Slightly reduce binary size by using the smaller 'rt' feature and the
current_thread runtime flavor in the installer, since there is no
benefit to true multithreading.

installer/src/main.rs

@@ -142,7 +142,7 @@ async fn run() -> Result<(), Error> {
     Ok(())
 }
 
-#[tokio::main]
+#[tokio::main(flavor = "current_thread")]
 async fn main() {
     if let Err(e) = run().await {
         eprintln!("{e:?}");