Support "exists" predicate for @IndexedEmbedded

Description

We're removing support for @IndexedEmbedded.indexNullAs in HSEARCH-2465.

As a result, users are no longer able to search for documents that have an object field present/missing.

We should support the concept of "exists" queries for object fields, or at least nested fields.

See https://www.elastic.co/guide/en/elasticsearch/guide/current/_dealing_with_null_values.html

Note: there are Search 5 tests that should pass when this ticket is resolved, and that are currently disabled in the pom.xml of the Elasticsearch module. Those tests will be (or have been) outlined as part of HSEARCH-2390.
Also, some relevant tests are disabled using the ElasticsearchSupportInProgress category.

Environment

None

Status

Assignee

Fabio Massimo Ercoli

Reporter

Yoann Rodière

Labels

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Suitable for new contributors

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Pull Request

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Feedback Requested

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Components

Fix versions

Affects versions

5.6.0.Beta3

Priority

Major
Configure