Surface option in the Blazor Web App template for WebAssembly interactivity

[danroth27]

Once we're ready for WebAssembly based interactivity and figured out the multitargeted single project model, we should surface the option in the Blazor Web App template to enable WebAssembly interactivity.

[danroth27]

Surfacing the Server interactivity option is tracked by #48626.

[mkArtakMSFT]

Marked as blocked as this is pending the multi-targeting work from the runtime team to land hopefully in preview 6.

[danroth27]

@mkArtakMSFT Now that we've decide to not go with a multitargeting approach for .NET 8, this is no longer blocked, correct?