chore: set 'stop VPN on quit' setting to true by default (#155)

It's fair to assume if you're closing Coder Desktop, you want Coder Connect to stop, so this is the default behaviour.

Tailscale also stops their VPN when quitting the app, even though it works fine with the app closed.

Author: ethanndickson

Coder-Desktop/Coder-Desktop/State.swift

@@ -55,7 +55,8 @@ class AppState: ObservableObject {
         }
     }
 
-    @Published var stopVPNOnQuit: Bool = UserDefaults.standard.bool(forKey: Keys.stopVPNOnQuit) {
+    // Defaults to `true`
+    @Published var stopVPNOnQuit: Bool = UserDefaults.standard.optionalBool(forKey: Keys.stopVPNOnQuit) ?? true {
         didSet {
             guard persistent else { return }
             UserDefaults.standard.set(stopVPNOnQuit, forKey: Keys.stopVPNOnQuit)
@@ -239,3 +240,14 @@ extension LiteralHeader {
         .init(name: name, value: value)
     }
 }
+
+extension UserDefaults {
+    // Unlike the exisitng `bool(forKey:)` method which returns `false` for both
+    // missing values this method can return `nil`.
+    func optionalBool(forKey key: String) -> Bool? {
+        guard object(forKey: key) != nil else {
+            return nil
+        }
+        return bool(forKey: key)
+    }
+}