Add auth token refresh to csharp

[BryanAldrich]

This adds a simple change to the AuthToken and TokenResponse code to allow for automatic refreshes. (I didn't test the refresh_token since I don't have one of those super handy).

Split off from #20233.

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[wing328]

Thanks for the PR but your commit (as shown in the Commits tab) is not linked to your Github account, which means this PR won't count as your contribution in https://github.com/OpenAPITools/openapi-generator/graphs/contributors.

Let me know if you need help fixing it.

Ref: https://github.com/OpenAPITools/openapi-generator/wiki/FAQ#how-can-i-update-commits-that-are-not-linked-to-my-github-account

[BryanAldrich]

Thanks for the PR but your commit (as shown in the Commits tab) is not linked to your Github account, which means this PR won't count as your contribution in https://github.com/OpenAPITools/openapi-generator/graphs/contributors.

Let me know if you need help fixing it.

Ref: https://github.com/OpenAPITools/openapi-generator/wiki/FAQ#how-can-i-update-commits-that-are-not-linked-to-my-github-account

Thanks, since I had to fix all that, I hit my mistake.. shh. nobody will know. (i'll fix the other PR I made as well..)

[wing328]

can you please review the build failure when you've time?

https://github.com/OpenAPITools/openapi-generator/actions/runs/12152223145/job/33889068846?pr=20234

[BryanAldrich]

Sorry i've had all these build failures, this is my first time working with this project, first time working with java since 2004 (yes, 20 years). I've scripted up checks on my side to prevent this again.

[wing328]

@BryanAldrich no problem. thanks for the PR.

the appveyor tests passed via https://ci.appveyor.com/project/WilliamCheng/openapi-generator/builds/51126886

[wing328]

PR merged. Let's give it a try.

Have a nice weekend