add awsappconfig example

[evbo]

Describe the feature

There currently is no example for integrating with appconfig, including how to appropriately cache, query specific versions of config, etc

Use Case

Please see discussion:

https://github.com/awslabs/aws-sdk-rust/discussions/856

Proposed Solution

No response

Other Information

No response

Acknowledgements

• [ ] I may be able to implement this feature request
• [ ] This feature might incur a breaking change

A note for the community

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