[VideoTranslation][csharp] Simplify C# client sample code, upgrade to…

… .net8.0 and support Linux for dotnet. (#2705)

* Update video translation client sample code.

* update namespace.

* Update readme.md

* Update option.

* i

* Make options class as partial.

* Change class to partial.

* Update app parameter.

* Fix warning.

* Fix warning.

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Co-authored-by: Yulin Li <[email protected]>