Add truncate timestamp annotation to BytesTransferByTagAndMetered

Now that buildStatsEvent method is generated automatically,
BytesTransferByTagAndMetered atom needs to be annotated to generate
ANNOTATION_ID_TRUNCATE_TIMESTAMP annotation.

Bug: 161569341
Test: m statslog-framework-java-gen
Test: atest UidAtomTests#testBytesTransferByTagAndMetered

Change-Id: I928220a27f6d43e78d57db24223650010eb4a74c