Java SDK 2.x: Mention the usage of ByteArrayDocument instead of BinaryDocuments to prevent memory issues

In our documentation https://docs.couchbase.com/java-sdk/2.7/document-operations.html#java-binary-document, when discussing BinaryDocuments, we do explain that these types can cause memory issues if not used correctly. We should however add to that alternative, which is to use ByteArrayDocument instead.