Create a Region Enum like the Java SDK

### Describe the feature

Create an Region Enum like Java SDK

### Use Case

I can use pattern matching to evaluate regions, and I don't need to refer to AWS documentation for region.

### 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

### Community Note
* Please vote on this issue by adding a 👍 [reaction](https://blog.github.com/2016-03-10-add-reactions-to-pull-requests-issues-and-comments/) to the original issue to help the community and maintainers prioritize this request
* Please do not leave "+1" or "me too" comments, they generate extra noise for issue followers and do not help prioritize the request
* If you are interested in working on this issue, please leave a comment

The issue names no files, tests, or Rust entry points; begin by locating how regions are represented in this repository and comparing that with the Java SDK. Confirm the supported region set and the expected pattern-matching API with maintainers. Done means a documented Rust Region enum is available without requiring users to consult AWS documentation.

Written by the indexing model from the issue text.