Aggregations should be a generic in responses

[delvedor]

As titled, this allows to write code like this:

import { Client } from '@elastic/elasticsearch'
import * as T from '@elastic/elasticsearch/lib/api/types'

const client = new Client({
  node: 'http://localhost:9200'
})

interface Document {
  world: number
}

interface Aggregation {
  hello: T.AggregationsValueAggregate
}

async function run () {
  const result = await client.search<Document, Aggregation>({
    index: 'foo',
    query: { match_all: {} },
    aggregations: {
      hello: {
        avg: {
          field: 'world'
        }
      }
    }
  })

  result.aggregations.hello // autocompletes to AggregationsValueAggregate
}

[mshustov]

Shouldn't we enforce TAggregations abide by Record<AggregateName, AggregationsAggregate> interface?
TAggregations extends Record<AggregateName, AggregationsAggregate> = Record<AggregateName, AggregationsAggregate>?
However,AggregationsAggregate is a union of types, I'm not sure it won't disrupt API consumers' code. We can do it in a follow-up.

[mshustov]

The overall approach looks good to me. Curious to hear @dgieselaar since the APM team has to work around the lack of aggregations typed parameter in the SearchResponse interface

[dgieselaar]

Works for me! Small change on our side.