Feat/Add support for weighted average aggregation

[atreids]

Issues

resolves #154

Aim

Add support for weight average aggregations released in v6.4.0 release notes

A weighted average is ∑(value * weight) / ∑(weight)

Solution

• Added new WeightedAverageAggregation class which extends MetricsAggregationBase.
• As the structure of the weight average aggregation is slightly different from other metric aggregations. Add two new methods value and weight to allow the user to set these metrics. The metric can be a string (for a field name), or a script. They both accept an optional second param to set the missing property. Alternatively, the user can set value and weight when constructing the class - but cannot set missing.
• Overwrote default methods script, field, and missing as these did not make sense as top level methods for this aggregation.
• Added a test.

Example

const weightedAvgAgg = esb.weightedAverageAggregation(
    'myWeightedAgg',
    'value_field',
    'weighted_field',
);
const body = esb.requestBodySearch().agg(weightedAvgAgg);

Would produce a query with:

{
  "aggs": {
    "myWeightedAgg": {
      "weighted_avg": {
        "value": {
          "field": "value_field"
        },
        "weight": {
          "field": "weighted_field"
        }
      }
    }
  }
}

Alternatively.

const weightedAvgAgg = new WeightedAverageAggregation('my_weighted_agg')
    .value('my_value_field', 5)
    .weight('my_weight_field', 10);
const body = new RequestBodySearch().agg(weightedAvgAgg);

Would produce a query with:

{
  "aggs": {
    "my_weighted_agg": {
      "weighted_avg": {
        "value": {
          "field": "my_value_field",
	  "missing": 5
        },
        "weight": {
          "field": "my_weight_field",
          "missing": 10
        }
      }
    }
  }
}

[sudo-suhas]

Thanks for the PR @atreids

[github-actions]

🎉 This PR is included in version 2.27.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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