Android Support (#166)

1. Add vpnservice tauri plugin for android.
2. add workflow for android.
3. Easytier Core support android, allow set tun fd.

tauri-plugin-vpnservice/build.rs

@@ -0,0 +1,14 @@
+const COMMANDS: &[&str] = &[
+    "ping",
+    "prepare_vpn",
+    "start_vpn",
+    "stop_vpn",
+    "register_listener",
+];
+
+fn main() {
+    tauri_plugin::Builder::new(COMMANDS)
+        .android_path("android")
+        .ios_path("ios")
+        .build();
+}