android: Add networkSecurityConfig to fetch CLRs/OCSP via HTTP

Android 9 restricts this to only HTTPS by default.

Fixes #3273.

src/frontends/android/app/src/main/AndroidManifest.xml

@@ -28,6 +28,7 @@
         android:icon="@mipmap/ic_launcher"
         android:label="@string/app_name"
         android:theme="@style/ApplicationTheme"
+        android:networkSecurityConfig="@xml/network_security_config"
         android:allowBackup="false" >
         <activity
             android:name=".ui.MainActivity"