Support @ElementCollection attribute mappings

https://github.com/introproventures/graphql-jpa-query/blob/master/graphql-jpa-query-boot-starter/src/test/java/com/introproventures/graphql/jpa/query/web/model/Book.java

//based upon https://www.callicoder.com/hibernate-spring-boot-jpa-element-collection-demo/ @ElementCollection @CollectionTable(name = "author_phone_numbers", joinColumns = @joincolumn(name = "author_id")) @column(name = "phone_number")
private Set phoneNumbers = new HashSet<>();

JPA's @ElementCollection annotation needs to mapped to GraphQL schema that wraps JPA collection persistent attribute with basic generic attribute type (including enum Jav a types ) into GraphQL List type field of scalar types. Only Basic persistent types are to be supported for now.

Given Author entity class that defines annotated @ElementCollection attribute phoneNumbers of basic type String

@Entity
@Getter
@Setter
@ToString
@EqualsAndHashCode(exclude={"books","phoneNumbers"}) // Fixes NPE in Hibernate when initializing lazy collections (See issue #1)
public class Author {
	@Id
	Long id;

	String name;

	@OneToMany(mappedBy="author")
	Collection<Book> books;
	
	@ElementCollection 
	@CollectionTable(name = "author_phone_numbers", joinColumns = @JoinColumn(name = "author_id")) 
	@Column(name = "phone_number")
	private Set<String> phoneNumbers = new HashSet<>();	
	
}

GraphQL Schema Builder needs to produce the following schema for Author type:

type Author {
     id: int
     name: String
     books: [Book]
     phoneNumbers: [String]
}

GraphQL query { Author(id: 1) { id name, phoneNumbers } } should return result below:

 {
      Author: {
           id:1, 
           name: "Leo Tolstoy",
           phoneNumbers: [
                 "1-123-1234", 
                 "1-123-5678"
           ]
      }
}