[FEATURE] Support bool query operators in Query DSL for object initializer syntax

[stevejgordon]

This is broken out from #6556.

Add support for combining queries created using the object initializer syntax into bool queries using the &&, ||, ! and + operators.

For example:

var search = new SearchRequest<Project>
{
    Query = new TermQuery(Infer.Field<Project>(p => p.Name)) { Value = "x" } ||
        new TermQuery(Infer.Field<Project>(p => p.Name)) { Value = "y" }
};

should produce:

{
  "query": {
    "bool": {
      "must": [
        {
          "term": {
            "name": {
              "value": "x"
            }
          }
        },
        {
          "term": {
            "name": {
              "value": "y"
            }
          }
        }
      ]
    }
  }
}