Verify SourceConfig and RepoConfig define at least one URL

[achilleas-k]

The following check happens when both creating a SourceConfig and a RepoConfig. Specifying none of the three should result in an error, since it makes for an unusable repository configuration.

osbuild-composer/internal/store/store.go

Lines 637 to 643 in 81240f5

	if s.Type == "yum-baseurl" {
	repo.BaseURLs = urls
	} else if s.Type == "yum-metalink" {
	repo.Metalink = s.URL
	} else if s.Type == "yum-mirrorlist" {
	repo.MirrorList = s.URL
	}

See also osbuild/osbuild#1411