Allow specifying a default Flatpak configuration (or use "Devel" if found)
Right now it seems that GNOME Builder picks the first Flatpak manifest it finds and uses that as the default for new projects.
Projects like Workbench have a dedicated manifest that is supposed to be used for development. We'd need a way to specify that these manifests should be used for projects by default.
Alternatively GNOME Builder should prefer "app-id.Devel.{json,yml}" manifests.