Refactor schema augmentation to have hooks for customization (#224)

Due to these changes, schema augmentation is no longer performed on the compiled graphql schema, but on the given type definitions. This will greatly simplify the extension of the neo4j schema with custom resolvers, such as with https://netflix.github.io/dgs/.

core/src/main/kotlin/org/neo4j/graphql/ExtensionFunctions.kt

@@ -1,23 +1,14 @@
 package org.neo4j.graphql
 
+import graphql.language.Description
 import graphql.language.VariableReference
-import graphql.schema.GraphQLArgument
-import graphql.schema.GraphQLInputType
-import graphql.schema.GraphQLType
 import org.neo4j.cypherdsl.core.*
+import java.util.*
 
 fun <T> Iterable<T>.joinNonEmpty(separator: CharSequence = ", ", prefix: CharSequence = "", postfix: CharSequence = "", limit: Int = -1, truncated: CharSequence = "...", transform: ((T) -> CharSequence)? = null): String {
     return if (iterator().hasNext()) joinTo(StringBuilder(), separator, prefix, postfix, limit, truncated, transform).toString() else ""
 }
 
-fun input(name: String, type: GraphQLType): GraphQLArgument {
-    return GraphQLArgument
-        .newArgument()
-        .name(name)
-        .type((type.ref() as? GraphQLInputType)
-                ?: throw IllegalArgumentException("${type.innerName()} is not allowed for input")).build()
-}
-
 fun queryParameter(value: Any?, vararg parts: String?): Parameter<Any> {
     val name = when (value) {
         is VariableReference -> value.name
@@ -36,3 +27,7 @@ fun PropertyContainer.id(): FunctionInvocation = when (this) {
 }
 
 fun String.toCamelCase(): String = Regex("[\\W_]([a-z])").replace(this) { it.groupValues[1].toUpperCase() }
+
+fun <T> Optional<T>.unwrap(): T? = orElse(null)
+
+fun String.asDescription() = Description(this, null, this.contains("\n"))