[Feature Contribution]: Upgrade to .net 9

[danuw]

What happened?

Upgrade to .net 9 framework

Code of Conduct

• I agree to follow this project's Code of Conduct

Feature Commitment

• I commit to contributing this feature as a PR and working with the GSF to merge this feature into the Carbon Aware SDK.

[danuw]

Interesting read for the swagger UI migration
https://codewithmukesh.com/blog/dotnet-swagger-alternatives-openapi/