WireguardApp: Add async variant of modify tunnel function

Signed-off-by: Alessio Nossa <alessio.nossa@gmail.com>

Sources/WireGuardApp/Tunnel/TunnelsManager.swift

@@ -206,6 +206,7 @@ class TunnelsManager {
         }
     }
 
+    @available(*, renamed: "modify(tunnel:tunnelConfiguration:onDemandOption:shouldEnsureOnDemandEnabled:)")
     func modify(tunnel: TunnelContainer, tunnelConfiguration: TunnelConfiguration,
                 onDemandOption: ActivateOnDemandOption,
                 shouldEnsureOnDemandEnabled: Bool = false,
@@ -299,6 +300,22 @@ class TunnelsManager {
         }
     }
 
+    @available(iOS 13.0, macOS 10.15.0, *)
+    func modify(tunnel: TunnelContainer, tunnelConfiguration: TunnelConfiguration,
+                onDemandOption: ActivateOnDemandOption,
+                shouldEnsureOnDemandEnabled: Bool = false) async throws {
+        return try await withCheckedThrowingContinuation { continuation in
+            modify(tunnel: tunnel, tunnelConfiguration: tunnelConfiguration, onDemandOption: onDemandOption, shouldEnsureOnDemandEnabled: shouldEnsureOnDemandEnabled) { error in
+                if let error = error {
+                    continuation.resume(throwing: error)
+                    return
+                }
+
+                continuation.resume(returning: ())
+            }
+        }
+    }
+
     func remove(tunnel: TunnelContainer, completionHandler: @escaping (TunnelsManagerError?) -> Void) {
         let tunnelProviderManager = tunnel.tunnelProvider
         #if os(macOS)