Disable identity column generation for the entire model

[nandor23]

Currently, there are methods to configure identity generation strategy globally (e.g. UseIdentityColumns(), UseIdentityAlwaysColumns()), which control whether the database generates values automatically or allows user-provided values. However, there's no way to disable database generation entirely and require that all identity values must be provided by the application.

It would be helpful to have a method like:

protected override void OnModelCreating(ModelBuilder modelBuilder)
    => modelBuilder.UseNoIdentityGeneration();