android/AndroidManifest.xml: enable requestLegacyExternalStorage

This is a workaround for the new scoped storage design in Android 11:

 https://developer.android.com/about/versions/11/privacy/storage

This needs a proper solution eventually, but this quick fix will do
until we change "targetSdkVersion" to 30.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1061

NEWS

@@ -10,6 +10,8 @@ ver 0.22.5 (not yet released)
   - pulse: fix deadlock with "always_on"
 * Windows:
   - enable https:// support (via Schannel)
+* Android
+  - work around "Permission denied" on mpd.conf
 
 ver 0.22.4 (2021/01/21)
 * protocol

android/AndroidManifest.xml

@@ -19,6 +19,7 @@
   <uses-permission android:name="android.permission.FOREGROUND_SERVICE" />
 
   <application android:allowBackup="true"
+               android:requestLegacyExternalStorage="true"
                android:icon="@drawable/icon"
                android:banner="@drawable/icon"
                android:label="@string/app_name">