pw_transfer: Add py_proto_library target for update_bundle_proto

Change-Id: I357cf3338a54c43786672e9d92034e916967b0ef
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/209731
Reviewed-by: Wyatt Hepler <hepler@google.com>
Lint: Lint 🤖 <android-build-ayeaye@system.gserviceaccount.com>
Commit-Queue: Dawn Cha <chadawn@google.com>
diff --git a/pw_software_update/BUILD.bazel b/pw_software_update/BUILD.bazel
index c2d3954..af09897 100644
--- a/pw_software_update/BUILD.bazel
+++ b/pw_software_update/BUILD.bazel
@@ -49,6 +49,11 @@
     deps = [":update_bundle_proto"],
 )
 
+py_proto_library(
+    name = "update_bundle_py_pb2",
+    deps = [":update_bundle_proto"],
+)
+
 java_lite_proto_library(
     name = "update_bundle_java_proto_lite",
     deps = [":update_bundle_proto"],