flatpaksigner: Support multiple applications per GitLab project
Okular comes in two flavors: Okular (widget-based for desktop systems) with application ID org.kde.okular
and Okular Kirigami (qml-based for mobile devices) with application ID org.kde.okular.kirigami
. The Flatpak bundles for those two apps will be built with separate GitLab jobs and we'll use separate Flatpak nightly repos for both apps, so that flatpaksigner will only have to deal with a single Flatpak bundle, but we have to allow specifying multiple application IDs per project in the project settings.