[SDK-2825] InAppMessages using Flutter Streams

_docs/_developer_guide/platform_integration_guides/flutter/inapp_messages.md

@@ -56,14 +56,40 @@ For an example, see [AppDelegate.swift](https://github.com/braze-inc/braze-flutt
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-## In-app message data callback
+## Receiving in-app message data
+
+To receive in-app message data in your Flutter app, the `BrazePlugin` supports sending in-app message data using [Dart Streams](https://dart.dev/tutorials/language/streams) (recommended) or by using a data callback (legacy).
+
+The `BrazeInAppMessage` object supports a subset of fields available in the native model objects, including `uri`, `message`, `header`, `buttons`, `extras`, and more.
+
+{% alert note %} The legacy data callback method will soon be deprecated. In-app messages can be added to both data streams and data callbacks. If you have already integrated data callbacks and wish to use data streams, remove any callback logic to ensure that in-app messages are processed exactly once. {% endalert %}
+
+### Method 1: In-app message data streams (recommended)
+
+You can set a data stream listener in Dart to receive in-app message data in your Flutter app.
+
+To begin listening to the stream, use the code below to create a `StreamSubscription` in your Flutter app and call the `subscribeToInAppMessages()` method with a function that takes a `BrazeInAppMessage` instance. Remember to `cancel()` the stream subscription when it is no longer needed.
+
+```dart
+// Create stream subscription
+StreamSubscription inAppMessageStreamSubscription;
+
+inAppMessageStreamSubscription = _braze.subscribeToInAppMessages((BrazeInAppMessage inAppMessage) {
+  // Function to handle in-app messages
+}
+
+// Cancel stream subscription
+inAppMessageStreamSubscription.cancel();
+```
+
+For an example, see [main.dart](https://github.com/Appboy/flutter-sdk/blob/develop/braze_plugin/example/lib/main.dart) in our sample app.
+
+### Method 2: In-app message data callback (Legacy)
 
 You can set a callback in Dart to receive Braze in-app message data in the Flutter host app.
 
 To set the callback, call `BrazePlugin.setBrazeInAppMessageCallback()` from your Flutter app with a function that takes a `BrazeInAppMessage` instance.
 
-The `BrazeInAppMessage` object supports a subset of fields available in the native model objects, including `uri`, `message`, `header`, `buttons`, `extras`, and more.
-
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@@ -81,7 +107,7 @@ For an example, see [AppDelegate.swift](https://github.com/braze-inc/braze-flutt
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-### Replaying the callback for in-app messages
+#### Replaying the callback for in-app messages
 
 To store any in-app messages triggered before the callback is available and replay them once it is set, add the following entry to the `customConfigs` map when intializing the `BrazePlugin`:
 ```dart