Drop Swashbuckle/Swagger UI, adopt OpenAPI for .NET 9 or later

[guardrex]

This is in a few 9.0 samples ...

https://github.com/search?q=repo%3Adotnet%2Fblazor-samples%20swashbuckle%20swagger&type=code

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• Content Source: dotnet/blazor-samples
• GitHub Login: @guardrex