JSON log filter plugin is not installed by default and it seems it cannot be installed through the Rundeck GUI. To install it manually enter the container
docker exec -it rundeck-docker sh
Enter the libext directory and download the jar file:
cd libext/ wget https://github.com/rundeck-plugins/jq-json-logfilter/releases/download/1.0.4/jq-json-logfilter-1.0.4.jar
You should now have the log filter in the Workflow under Global log filters