Add support for custom scalars

[shubhamprshr27]

Can we think about adding support for scalars as well?

This shall help speed up development and validations.

[TArch64]

+1 It will be great to be able to validate an array of UUIDs

Example in nestjs graphql. GraphQLUUID is a type from graphql-type-uuid

@Field(returns => [GraphQLUUID])
@Directive('@constraint(minItems: 1)')
public categories: string[];