Add inference-based overload to ForNpgsqlHasEnum

[austindrenski]

Current

public static ModelBuilder ForNpgsqlHasEnum(
 [NotNull] this ModelBuilder modelBuilder, 
 [CanBeNull] string schema, 
 [NotNull] string name, 
 [NotNull] string[] labels);

public static ModelBuilder ForNpgsqlHasEnum(
 [NotNull] this ModelBuilder modelBuilder, 
 [NotNull] string name, 
 [NotNull] string[] labels);

Proposed additions

public static ModelBuilder ForNpgsqlHasEnum<TEnum>(
 [NotNull] this ModelBuilder modelBuilder, 
 [CanBeNull] string schema = null,
 [CanBeNull] string name = null,
 [CanBeNull] INpgsqlNameTranslator nameTranslator = null) 
 where TEnum : struct, Enum;

• nameTranslator is used when name is null
• nameTranslator is used when labels is null.
  • Should default (internally) to match the default in MapEnum<T>.

edit: Removing labels proposal. Too much complexity, not enough upside.

[YohDeadfall]

I thought to request it today, but you beat me (: