[federation] fix @key fed v2 definition

Missed default value for the `resolvable` argument. Updated definition

```kotlin
directive @key(fields: _FieldSet!, resolvable: Boolean = true) repeatable on OBJECT | INTERFACE
```

Author: dariuszkuc

generator/graphql-kotlin-federation/src/main/kotlin/com/expediagroup/graphql/generator/federation/directives/KeyDirective.kt

@@ -116,6 +116,7 @@ internal val KEY_DIRECTIVE_TYPE_V2: graphql.schema.GraphQLDirective = graphql.sc
         GraphQLArgument.newArgument()
             .name("resolvable")
             .type(Scalars.GraphQLBoolean)
+            .defaultValueProgrammatic(true)
     )
     .repeatable(true)
     .build()

generator/graphql-kotlin-federation/src/test/kotlin/com/expediagroup/graphql/generator/federation/FederatedSchemaV2GeneratorTest.kt

@@ -55,7 +55,7 @@ private val FEDERATED_SDL_V2 =
       ) on FIELD | FRAGMENT_SPREAD | INLINE_FRAGMENT
 
     "Space separated list of primary keys needed to access federated object"
-    directive @key(fields: _FieldSet!, resolvable: Boolean) repeatable on OBJECT | INTERFACE
+    directive @key(fields: _FieldSet!, resolvable: Boolean = true) repeatable on OBJECT | INTERFACE
 
     "Links definitions within the document to external schemas."
     directive @link(import: [String], url: String) repeatable on SCHEMA