Add ab_ota_partitions prop to android_device

This will be used to generate ab_partitions.txt file in
target_files.zip

Test: Built soong target_files.zip locally
Bug: 388633394
Change-Id: I442c0907094abb4f68fb0c666efae52509aa9538
diff --git a/android/variable.go b/android/variable.go
index 4867067..419f778 100644
--- a/android/variable.go
+++ b/android/variable.go
@@ -664,6 +664,7 @@
 	ProductVirtualAbCompressionFactor string                                   `json:",omitempty"`
 	ProductVirtualAbCowVersion        string                                   `json:",omitempty"`
 	AbOtaUpdater                      bool                                     `json:",omitempty"`
+	AbOtaPartitions                   []string                                 `json:",omitempty"`
 
 	// Avb (android verified boot) stuff
 	BoardAvbEnable          bool                                `json:",omitempty"`