[Pre6] Blazor preloading change

[maraf]

PR dotnet/aspnetcore#62225 (preview 6)

We changed how we do preloading. Instead of using link headers, we have switched to <LinkPreload /> component.
The reasons for this change are

1. Having a component, we can rely on <base href="..." /> tag to correctly identify the "root" of blazor application within ASP.NET Core app.
2. Having a component, it's easy to turn the feature off, just remove the component.

The change requires a change to user applications by placing component somewhere near after the base tag

<base href="/" />
+<LinkPreload />