Description of problem:

Please add 'Flathub uses OSTree, which is not a supported content type in Red Hat Satellite' in our official documentation so it is not misleading to the customer

https://docs.redhat.com/en/documentation/red_hat_satellite/6.17/html-single/managing_content/index#managing-flatpak-repositories-in-project
 
 https://docs.redhat.com/en/documentation/red_hat_satellite/6.18/html-single/managing_content/index#managing-flatpak-repositories-in-project

ref: https://access.redhat.com/solutions/4460251

How reproducible:

100%

Business Impact / Additional info:

The customer may try to sync from https://flathub.org without knowing it is not supported