Enhance Validation Behavior Pipeline

[thanhbao0408]

This enhancement lets you have the flexibility for not ading the IAbstractValidator implementation to every handler message.
Also, it lets you inject services into the constructor of the validator

// You don't need to add a Validator class if the validation logic is empty
    public class CreateCustomer
    {
        public record Command : ICreateCommand<Command.CreateCustomerModel, CustomerDto>
        {
            public CreateCustomerModel Model { get; init; } = default!;

            public record CreateCustomerModel(string FirstName, string LastName, string Email, Guid CountryId);

            //internal class Validator : AbstractValidator<Command>
            //{
            //    public Validator()
            //    {
            //    }
            //}
        }
    }

// You can inject services here for validating
internal class Validator : AbstractValidator<Command>
{
    public Validator(IRepository<Product> _productRepo)
    {
        // use the repo for checking some database condition
    }
}