Improve updater setup

[clearlysid]

Hmm, wondering why not just do a simple

 "check_updates" => {
                    let w = app.get_window("main").unwrap();
                    w.trigger_global("tauri://update", None);
                }    

and let Tauri handle the rest? @clearlysid

Originally posted by @rajatkulkarni95 in #42 (comment)

[rajatkulkarni95]

You can also trigger this with the same tauri://update string on the FE, and do it with a setInterval if you want periodic checks instead of just on startup or explicit click.

I do all 3 for Octarine, with periodic being every few hours. Since I'm assuming Helmer would likely be an always open app, so waiting on the user to click update might be less fruitful if you push multiple updates in a week!