Add flag for automatic back pagination feature

libraries/featureflag/api/src/main/kotlin/io/element/android/libraries/featureflag/api/FeatureFlags.kt

@@ -161,4 +161,12 @@ enum class FeatureFlags(
         defaultValue = { false },
         isFinished = false,
     ),
+    AutomaticBackPagination(
+        key = "feature.automatic_back_pagination",
+        title = "Automatic back pagination of rooms",
+        description = "Allow the app to automatically back paginate in rooms to pre-fetch older messages in background." +
+            "\nRequires an app restart to take effect.",
+        defaultValue = { false },
+        isFinished = false,
+    ),
 }

libraries/matrix/impl/src/main/kotlin/io/element/android/libraries/matrix/impl/RustMatrixClientFactory.kt

@@ -105,6 +105,11 @@ class RustMatrixClientFactory(
     suspend fun create(client: Client): RustMatrixClient {
         val (anonymizedAccessToken, anonymizedRefreshToken) = client.session().anonymizedTokens()
 
+        // Must be called before creating the sync service, timelines etc.
+        if (featureFlagService.isFeatureEnabled(FeatureFlags.AutomaticBackPagination)) {
+            client.enableAutomaticBackpagination()
+        }
+
         client.setUtdDelegate(UtdTracker(analyticsService))
 
         val syncService = client.syncService()