Support "multi_terms" Aggregation

[sanvir10]

Elasticsearch add new type of Aggregation in version 7.12:
https://www.elastic.co/guide/en/elasticsearch//reference/master/search-aggregations-bucket-multi-terms-aggregation.html

Regards.

[sudo-suhas]

@sanvir10 would you be interested in creating a PR for the same?

[miralaur]

something like this:
class MultiTerms extends Aggregation {
constructor(name) {
super(name, 'multi_terms');
this._aggsDef.terms = [];
}

terms(terms) {
this._aggsDef.terms = [...terms];
return this;
}
}

[skined90]

Any update on this one?