Add C++20 modules support

### Describe the feature

Hi,
I'm not a user of aws-sdk-cpp, but I'm tracking the progress of c++20 modules support on https://arewemodulesyet.org/ and this is the issue we are linking to in our table of c++20 modules support.

### Use Case

Modules are part of C++20 and should greatly increase compile times, see https://en.cppreference.com/w/cpp/language/modules

### Proposed Solution

_No response_

### Other Information

_No response_

### Acknowledgements

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