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/android/src/test/java/ExampleUnitTest.kt

@@ -0,0 +1,17 @@
+package com.plugin.vpnservice
+
+import org.junit.Test
+
+import org.junit.Assert.*
+
+/**
+ * Example local unit test, which will execute on the development machine (host).
+ *
+ * See [testing documentation](http://d.android.com/tools/testing).
+ */
+class ExampleUnitTest {
+    @Test
+    fun addition_isCorrect() {
+        assertEquals(4, 2 + 2)
+    }
+}