Pre-install KeepSecret

This will replace the old KWalletManager app, which I've proposed for
removal in
https://invent.kde.org/kde-linux/kde-linux-packages/-/merge_requests/91.

mkosi.extra/usr/lib/install-flatpaks

@@ -4,4 +4,4 @@
 
 set -eux
 
-flatpak install --noninteractive --assumeyes --sideload-repo=/usr/share/factory/var/lib/flatpak/.ostree/repo org.gtk.Gtk3theme.Breeze org.kde.gwenview org.kde.okular org.kde.kwrite org.kde.haruna org.kde.qrca org.kde.ark org.kde.kcalc org.mozilla.firefox
+flatpak install --noninteractive --assumeyes --sideload-repo=/usr/share/factory/var/lib/flatpak/.ostree/repo org.gtk.Gtk3theme.Breeze org.kde.gwenview org.kde.okular org.kde.kwrite org.kde.haruna org.kde.qrca org.kde.ark org.kde.kcalc org.kde.keepsecret org.mozilla.firefox

mkosi.postinst.chroot

@@ -84,6 +84,7 @@ download_flatpaks() {
         ark
         gwenview
         kcalc
+        keepsecret
         haruna
         okular
         qrca