Support AWS KMS grant tokens

There is no simple support for AWS KMS grant tokens.
Customers can extend `DirectKmsMaterialProvider`
and override the `generateDataKey` or the appropriate AWS KMS call.

see
https://github.com/aws/aws-dynamodb-encryption-java/blob/41ad9bf0e06b9da8dab83cb9d804d3eb68ef29f5/sdk1/src/main/java/com/amazonaws/services/dynamodbv2/datamodeling/encryption/providers/DirectKmsMaterialProvider.java#L250

从 sdk1/src/main/java/com/amazonaws/services/dynamodbv2/datamodeling/encryption/providers/DirectKmsMaterialProvider.java 中提到的 generateDataKey 或适当的 AWS KMS 调用开始。跟踪该调用的执行方式，并确定调用方提供 grant token 的预期方式。当 DirectKmsMaterialProvider 能够简单地支持 AWS KMS grant token，且不要求客户重写 provider 时，即视为完成。

由索引模型根据 Issue 内容生成。