feat(react-native-webrtc): add config mod for Android minSdkVersion 24

Summary:
react-native-webrtc requires that the Android minSdkVersion is
set to 24.
Related issue on this here and also mentioned on Daily's RN SDK
that has react-native-webrtc as a dependency.

Adds withBuildScriptExtMinimumVersion same as the ffmpeg-kit-react-native
config plugin. Maybe withBuildScriptExtMinimumVersion could be
exported in `config-plugins` package so that it could be used directly.

Author: thorbenprimke

packages/react-native-webrtc/README.md

@@ -59,7 +59,10 @@ export default {
 };
 ```
 
-This plugin will also disable desugaring in the Android `gradle.properties`: `android.enableDexingArtifactTransform.desugaring=false`, and disable iOS Bitcode for "Release" builds (required).
+## Important Notes
+
+- For iOS, this plugin disables Bitcodes for all builds (required).
+- For Android, this plugin disables desugaring in `gradle.properties`: `android.enableDexingArtifactTransform.desugaring=false` and the [minimum deployment target is changed to `24`](https://github.com/react-native-webrtc/react-native-webrtc/issues/720#issuecomment-552374206) (from `21`) which may break other packages in your app!
 
 ## Manual Setup
 

packages/react-native-webrtc/build/withWebRTC.js

@@ -31,7 +31,12 @@ const withWebRTC: ConfigPlugin<IOSPermissionsProps | void> = (
     "android.permission.SYSTEM_ALERT_WINDOW",
     "android.permission.WAKE_LOCK",
   ]);
-
+  config = AndroidConfig.Version.withBuildScriptExtMinimumVersion(config,
+    {
+      name: "minSdkVersion",
+      minVersion: 24,
+    }
+  )
   config = withDesugaring(config, true);
 
   return config;