Refresh scaffolded pilet

[FlorianRappl]

Right now the scaffolded pilet is a bit "too sticky". In order to apply, e.g., an update of the Piral instance / emulator package, you'd need to manually go to the pilet's directory and run pilet upgrade. Sure, this is the "usual" way, however, for a Blazor Pilet (Blazelet?) it should not be necessary. Ideally, this can be done directly from Visual Studio - and even better: it may even be implicit.

We should add at least a task to do that, but maybe even automate it appropriately. Easiest way would be to have something like <PiralInstanceVersion> in the csproj, such that it is (by default set to) "latest" (which auto-checks), but could also be set to anything else (and, e.g., in case of explicit versions may only check if the version match, resulting in an update of the scaffolded pilet, or not).