Add manifests for HeliumOS

[imbev]

Resolves #770

[hanthor]

Do we want to add manifests for all custom images? I can imageing the list becoming very long. Or should there be some way to pass it in to the build?

[supakeen]

Do we want to add manifests for all custom images? I can imageing the list becoming very long. Or should there be some way to pass it in to the build?

Probably a bit of both; I see no real necessity to add these definitions if they're going to be symlinks to centos-9 so perhaps something nice would be possible there so these types of PRs are necessary only for actual new distros.

cc @mvo5.