fix(GH-198): adedd support for fetching optional element collections elements

[igdianov]

This PR fixes fetching plural attributes annotated with @ElementCollection to use left outer join that makes collection elements optional should associated collection elements data set be empty, i.e. given

public class Author {
	@Id
	Long id;

	String name;

	@OneToMany(mappedBy="author", fetch=FetchType.LAZY)
	@OrderBy("id ASC")
	Set<Book> books;
	
	@ElementCollection(fetch=FetchType.LAZY) 
	@CollectionTable(name = "author_phone_numbers", joinColumns = @JoinColumn(name = "author_id")) 
	@Column(name = "phone_number")
	private Set<String> phoneNumbers = new HashSet<>();	
	
	@Enumerated(EnumType.STRING)
	Genre genre;	
}

When executing the following query with author containing empty phoneNumbers selection:

query {
  Author(id: 8) {
    id
    name
    phoneNumbers
    books {
      id
      title
      tags
    }
  }
}

The expected result should return the following Json:

{
  "data": {
    "Author": {
      "id": 8,
      "name": "Igor Dianov",
      "phoneNumbers": [],
      "books": []
    },
  }
}

It is also possible to use where criteria expressions to fetch the selection that satisfies search criteria with values in the element collection, i.e. given query,

query {
  Books(where: {tags: {EQ: "war"}}) {
    select {
      id
      title
      tags
    }
  }
}

The expected result should be

{
  "data": {
    "Books": {
      "select": [
        {
          "id": 2,
          "title": "War and Peace",
          "tags": [
            "piece",
            "war"
          ]
        }
      ]
    }
  }
}

Also fixes #198

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@9854252). Click here to learn what that means.
The diff coverage is 50%.

@@            Coverage Diff            @@
##             master     #200   +/-   ##
=========================================
  Coverage          ?   73.67%           
  Complexity        ?      877           
=========================================
  Files             ?       50           
  Lines             ?     3708           
  Branches          ?      626           
=========================================
  Hits              ?     2732           
  Misses            ?      698           
  Partials          ?      278

Impacted Files	Coverage Δ	Complexity Δ
...ures/graphql/jpa/query/schema/model/book/Book.java	0% <0%> (ø)	0 <0> (?)
...a/query/schema/impl/QraphQLJpaBaseDataFetcher.java	75.82% <100%> (ø)	170 <0> (?)

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