Search performance issue when using Elasticsearch [7.7.0, 7.8.x]

[cmark]

Describe the bug
Significant performance drop in searches/aggregations when using Elasticsearch 7.7.0+ in Snow Owl 7.7.0+ release.

To Reproduce

Run a validation rule that uses either a search or aggregation with a large number of terms filter values (all active concept IDs listed, huge ECL/QL result set, etc.).

Expected behavior
Running any search with large number of term filter values should not cause significant performance drop in computation time.

Version

• Snow Owl Version: 7.7.0, 7.8.0
• Elasticsearch Version (external): 7.7.0, 7.8.0

Additional context
Elasticsearch PR where the Percolator FetchPhase implementation rewrite happened:
elastic/elasticsearch#53728
Lucene 8.6.0 PR where the potential fix has been introduced:
apache/lucene-solr#1465
Related Elastic.co Discussion:
https://discuss.elastic.co/t/performance-problem-in-percolator-fetch-phase-classes/243748

This performance issue is going to be fixed when Elasticsearch 7.9.0 releases (it uses Lucene 8.6.0 under the hood).

[cmark]

Elasticsearch 7.9.0 is available, and Snow Owl now supports that, resolving as fixed.