Clarify that number of threads is set by packages
Clarify that number of threads is set by packages

This commit clarifies that on systemd the packages already set the number of
threads for the Elasticsearch process.

Relates #27840

strapdata/elassandra,vroyer/elasticassandra,vroyer/elasticassandra,vroyer/elassandra,strapdata/elassandra,strapdata/elassandra,vroyer/elassandra,vroyer/elassandra,strapdata/elassandra,strapdata/elassandra,vroyer/elasticassandra