add search after parameter

[sinkyoungdeok]

I understood that the 'search after' feature exists for indexing purposes.
However, 'search after' is also necessary for supporting pagination, and for this reason, we will be adding the 'search after' parameter.
Please refer to the following Elasticsearch official documentation for more information: https://www.elastic.co/guide/en/elasticsearch/reference/current/paginate-search-results.html