fix: add support for nested where criteria expressions

[igdianov]

This PR adds support for nested where criteria expressions, i.e. given query

query { 
  Humans {        
    select {
      id
      name
      homePlanet
      favoriteDroid {
        name
        primaryFunction(where:{function:{EQ:"Astromech"}}) {
          function
        }
      }
    }
  }  
}

Will result in

{
  "data": {
    "Humans": {
      "select": [
        {
          "id": "1001",
          "name": "Darth Vader",
          "homePlanet": "Tatooine",
          "favoriteDroid": {
            "name": "R2-D2",
            "primaryFunction": {
              "function": "Astromech"
            }
          }
        }
      ]
    }
  }
}

[codecov]

Codecov Report

Merging #148 into master will increase coverage by 0.08%.
The diff coverage is 92.5%.

@@             Coverage Diff              @@
##             master     #148      +/-   ##
============================================
+ Coverage     68.28%   68.36%   +0.08%     
+ Complexity      443      442       -1     
============================================
  Files            33       33              
  Lines          2248     2254       +6     
  Branches        336      337       +1     
============================================
+ Hits           1535     1541       +6     
  Misses          577      577              
  Partials        136      136

Impacted Files	Coverage Δ	Complexity Δ
...ry/schema/impl/GraphQLJpaOneToManyDataFetcher.java	73.77% <100%> (-0.08%)	11 <0> (-4)
...jpa/query/schema/impl/GraphQLJpaSchemaBuilder.java	87.67% <100%> (+0.02%)	120 <0> (+1)	⬆️
...a/query/schema/impl/QraphQLJpaBaseDataFetcher.java	71.65% <91.89%> (+0.31%)	149 <10> (+2)	⬆️

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