Custom mirrow list for Glance Simplestreams Sync

I would like to add debian cloud images to simplestream sync, but documentation is not very useful on how to modify the default YAML-formatted list.

{url: ‘‘Ubuntu Cloud Images’’, name_prefix: ‘‘ubuntu:released’’, path: ‘‘streams/v1/index.sjson’’, max: 1, item_filters: [’‘release~(trusty|xenial|bionic|focal)’’, ‘‘arch~(x86_64|amd64)’’, ‘‘ftype~(disk1.img|disk.img)’’]}

Can someone point me in the right direction?

no one? really ?