migrated BlazorServer to Blazor web app

[maxmantz]

What issue does this PR address?

In my quest to migrate my own app to .NET 8 and using your sample app as a base for comparison, I've decided to migrate your sample to a Blazor web app as per this guide. Since this will be the way Blazor Server apps are built from .NET 8 onwards, I think it would be a good idea to update the sample as well to reflect these changes.

I checked everything and it works as before. I've also added an authentication check to Index.razor to see whether or not the app keeps an active session alive.

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