Add migration docs for GC logging
Add migration docs for GC logging

This commit adds a note to the 6.2 docs for the addition of
out-of-the-box GC logging.

Relates #27631

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