The search operator runs a search via ElasticSearch client given a query.
It takes a dictionary as input, which should be written in [Query DSL](https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl.html).
To use this operator, you need to [set up ElasticSearch](https://www.elastic.co/guide/en/elasticsearch/reference/current/setup.html) in advance.
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## Code Example
With an example ElasticSearch client 'localhost:9200',
search across the index 'test_index' using an example query `{'match_all': {}}` to get all documents.