Add support for terminate_after parameter

[dani-sc]

Elasticsearch offers a terminate_after parameter:

(Optional, integer) Maximum number of documents to collect for each shard. If a query reaches this limit, Elasticsearch terminates the query early. Elasticsearch collects documents before sorting.

[src]

This pull request adds support for this option in Elasticsearch::DSL::Search::Options::DSL_METHODS.

[cla-checker-service]

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