Publish flatpak application for tryton
It has been discussed on https://discuss.tryton.org/t/add-desktop-build-for-linux/927
review390041002 is an initial prototype to build flatpak for tryton-6.2.4. It requires review390051002 because flatpak requires a minimum of 3 levels for the application ID (otherwise the DBus registration of Main application is forbidden as the root path is not the same flatpak application ID). Also the TMPDIR must adapted to allow other application to open them.
I propose to publish it on flathub but I do not know yet how to deal with the multiple series, so I asked on the forum: https://discourse.flathub.org/t/how-to-publish-multiple-major-version/2205.