DynamoDBIO misses writing items if `withDeduplicateKeys` is not set

A new method `withDeduplicateKeys` was added in DynamoDBIO from 2.27.0. It feels like it is optional according to the doc, and it was not shown in the examples either. But if a key name not set by it, the deduplication logic still takes effect but uses an empty map as the `Map<String, AttributeValue>` part of the deduplication key, which results in all items having the same key and being deduplicated, writing only the last item to DynamoDB.

I think we need to add an check on DeduplicateKeys in `extractDeduplicateKeyValues`, and skip the deduplication logic if it's empty.