fix(GH-273): detach result entities from entity manager persistent context

[igdianov]

Fixes #273

[codecov]

Codecov Report

Merging #275 into master will increase coverage by 0.00%.
The diff coverage is 83.33%.

@@            Coverage Diff            @@
##             master     #275   +/-   ##
=========================================
  Coverage     74.02%   74.02%           
  Complexity     1070     1070           
=========================================
  Files            72       72           
  Lines          4750     4754    +4     
  Branches        679      680    +1     
=========================================
+ Hits           3516     3519    +3     
  Misses          934      934           
- Partials        300      301    +1     

Impacted Files	Coverage Δ	Complexity Δ
.../jpa/query/schema/impl/GraphQLJpaQueryFactory.java	78.89% <83.33%> (-0.02%)	229.00 <0.00> (ø)

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[hump]

look good, no caching effect with this PR.
Tested with graphql-jpa-query-example-simple:
query with graphiql:

{
  Humans {
    select {
      name
    }
  }
}

Result:

{
  "data": {
    "Humans": {
      "select": [
        {
          "name": "Luke Skywalker"
        },
        {
          "name": "Darth Vader"
        },
        {
          "name": "Han Solo"
        },
        {
          "name": "Leia Organa"
        },
        {
          "name": "Wilhuff Tarkin"
        }
      ]
    }
  }
}

change name with h2-console

Result:

{
  "data": {
    "Humans": {
      "select": [
        {
          "name": "Luky Skywalker"
        },
        {
          "name": "Darth Vader"
        },
        {
          "name": "Han Solo"
        },
        {
          "name": "Leia Organa"
        },
        {
          "name": "Wilhuff Tarkin"
        }
      ]
    }
  }
}```

[hump]

But - Caching effect remains for this query (single record with id):

{
  Human(id: "1000") {
    name
  }
}