Add examples for ENUMs implementations

I am trying to add Enums for the schema in the `.graphqls` file but I see that version 4 doesn't include any thing related to the [GraphQL Enums](https://graphql.org/learn/schema/#enumeration-types) while previous version 3 includes [Enum](https://github.com/drupal-graphql/graphql/tree/8.x-3.x/src/Plugin/GraphQL/Enums) implementations like [graphql_responsive_image](https://git.drupalcode.org/project/graphql_responsive_image/-/blob/8.x-1.x/src/Plugin/GraphQL/Fields/Entity/Fields/Image/ResponsiveImageStructured.php?ref_type=heads#L24) implemented such thing.

I am not a graphql expert so may be I am missing it in the documenation so please guide me regarding it.