IBX-6827: Aggregation API improvements #1481

Job	Run time
Solr integration tests (7.4)	9m 57s
Solr integration tests (8.0)	11m 19s
Run code style check (8.0)	2m 32s
Unit tests & SQLite integration tests (7.4)	7m 1s
Solr integration tests (8.1)	9m 42s
Unit tests & SQLite integration tests (8.0)	7m 7s
Unit tests & SQLite integration tests (8.1)	6m 55s
PostgreSQL integration tests (7.4)	19m 22s
MySQL integration tests (7.4)	12m 59s
PostgreSQL integration tests (8.0)	20m 32s
MySQL integration tests (8.0)	12m 45s
PostgreSQL integration tests (8.1)	21m 11s
MySQL integration tests (8.1)	12m 39s
	2h 34m 1s

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