feat: add GDM customization

disable fingerprint and smartcard login
add a banner text and logo on login screen

debian/install

@@ -0,0 +1,2 @@
+etc
+usr

debian/postinst

@@ -3,6 +3,10 @@ set -e
 
 case "$1" in
     configure)
+        # enable GDM customization
+        if [ -x /usr/bin/dconf ] ; then
+            dconf update
+        fi
         # Configure PAM for credential cache 
         apt-mark manual libpam-ccreds >/dev/null || true
         if [ -e /usr/share/pam-configs/ccreds-check ] ; then

debian/postrm

@@ -0,0 +1,23 @@
+#!/bin/sh
+set -e
+
+case "$1" in
+    purge)
+        # forget GDM customization
+        if [ -x /usr/bin/dconf ] ; then
+            dconf update
+        fi
+    ;;
+    remove|upgrade|failed-upgrade|abort-install|abort-upgrade|disappear)
+    ;;
+
+    *)
+        echo "postrm called with unknown argument \`$1'" >&2
+        exit 1
+    ;;
+esac
+
+
+#DEBHELPER#
+
+exit 0