Support for iteration over composite aggregation responses

[jgough]

There doesn't seem to be an automatic way to iterate over composite aggregation responses: https://www.elastic.co/guide/en/elasticsearch/reference/7.6/search-aggregations-bucket-composite-aggregation.html

This is done by taking the after_key field and then feeding it back to the next request via the after parameter - much like the scroll API.

Would be a very useful feature to have this rather than having to manually pass these around and keep making queries.

[magical-travvo]

We're having the same issue, it would be good to be able to do this without creating something external to Elasticsearch, which would defeat the purpose of using Watcher.