TMDM-7868: "Modify time-based service to include a 'top' parameter"

Event statistics: add new "top" parameter to return the top N results.
(https://jira.talendforge.org/browse/TMDM-7868)
Initial commit for orderBy(count(...)) query support.

Adds option for OrderBy to use Count as parameter.
Adds Count option to get a Field as parameter.
Log visitor updates.
Adds unit test for feature test (order by occurrence count of "firstname" value in test data).
Amends existing tests (as a new Person instance was added).
TMDM-7868: "Modify time-based service to include a 'top' parameter"

Journal statistics:
* Takes advantage of new orderBy(count(...)) query operator in journal statistics.
* Gets the top N types present in repository.
* Ensures the "Concept" field is automatically indexed (since journal statistics does a orderBy(count("Concept"))).
* Clean up in top parameter handling.
* Adds cache for "top N" types query.
(https://jira.talendforge.org/browse/TMDM-7868)
Merge branch 'maintenance/5.6'