Document how to compensate for conventions different in EF Core than EF6

[ajcvickers]

For example, shadow FK property names in EF Core are PrincipalId rather than the Principal_Id name used by independent associations in EF6. This can be fixed with something like:

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    // Other model building here...
    
    foreach (var foreignKey in modelBuilder.Model.GetEntityTypes().SelectMany(e => e.GetDeclaredForeignKeys()))
    {
        // Note that something different would be needed for composite keys
        if (foreignKey.Properties.Count == 1)
        {
            foreignKey.Properties[0].SetColumnName(foreignKey.PrincipalEntityType.Name + "_Id");
        }
    }
}

[AndriySvyryd]

Related: #1989