[8.19] Expand docs about `executor` param in `SubscribableListener` (#127746)#127870

elasticsearchmachine merged 1 commit intoelastic:8.19elastic/elasticsearch:8.19from

DaveCTurner:backport/8.19/pr-127746DaveCTurner/elasticsearch:backport/8.19/pr-127746Copy head branch name to clipboard