Add example for using CachingMostRecentProvider and upgrading material version

### Problem:

The AWS docs mention "rotating cryptographic material" here: https://docs.aws.amazon.com/dynamodb-encryption-client/latest/devguide/most-recent-provider.html

However it could be more clear what "call the provider store's Create New Provider operation with the material name of the Most Recent Provider" means for this library.

### Solution:

This repo should have an example showing how to do this using the Metastore's newProvider() method.

### Out of scope:

Updating the corresponding AWS docs to reference this new example.

首先阅读链接的 AWS most-recent-provider 指南和 Metastore.newProvider() 入口点。添加一个 repository 示例，演示使用 CachingMostRecentProvider 并升级 material 版本，同时按要求保持 AWS 文档不变。

由索引模型根据 Issue 内容生成。