Mutations via updateById overwrite arrays instead of appending to them

It should be possible to append to array fields per [this elastic.co doc](https://www.elastic.co/guide/en/elasticsearch/reference/current/docs-update.html#_scripted_updates). Currently, the request is made to `/_update` with a `doc` object, but for appending to arrays we would need to be able to make a GraphQL request that is resolved to a `script` object.