docs: include name when creating GraphQLEnumValueDefinition (#2078)

### 📝 Description

Was using the docs and this caught me out, you have to set the enum name
when building a new GraphQLEnumValueDefinition otherwise you will
receive `Name must be non-null, non-empty and match
[_A-Za-z][_0-9A-Za-z]* - was 'null'`

### 🔗 Related Issues

Author: LtTempletonPeck

website/docs/schema-generator/writing-schemas/enums.md

@@ -46,6 +46,7 @@ val statusEnumType = GraphQLEnumType.newEnum()
     .name("Status")
     .values(Status.values().map {
       GraphQLEnumValueDefinition.newEnumValueDefinition()
+          .name(it.name)
           .value(it.name)
           .build()
     })