Currently koji does not record the packages installed in the livecd that is created when using createlivemedia. see https://koji.fedoraproject.org/koji/taskinfo?taskID=34097984 as an example task. The data is recorded in anaconda-packaging.log though it would need to be parsed and extracted. Another way to get the data to be recorded is querying the rpm database inside the livecd. you would need to do something like

# mkdir /tmp/iso /tmp/rootfs /tmp/squashfs
# mount -o loop Fedora-Workstation-Live-x86_64-30-20190408.n.0.iso  /tmp/iso
# mount /tmp/iso/LiveOS/squashfs.img /tmp/squashfs/ -t squashfs -o loop 
# mount -o loop /tmp/squashfs/LiveOS/rootfs.img /tmp/rootfs/
# rpm --dbpath /tmp/rootfs/var/lib/rpm/ -qa --qf "necesarry formating for the output"