fix: add greetd netinstall group for online DM selection

The packagechooser_dm.conf has greetd as a DM option with
method: netinstall-select, but no matching 'greetd' group existed
in /etc/calamares/modules/netinstall.yaml (which is what Calamares
loads in online mode via modules-search: [local] resolution).

Without the group, selecting greetd silently fails and the
displaymanager module falls back to SDDM instead.

Add greetd + greetd-dinit group alongside the existing SDDM,
LightDM, LXDM, LY groups.

iso-profiles/antergos/live-overlay/etc/calamares/modules/netinstall.yaml

@@ -272,6 +272,13 @@
     - lxdm
     - lxdm-dinit
 
+- name: "greetd"
+  description: "greetd display manager"
+  selected: false
+  packages:
+    - greetd
+    - greetd-dinit
+
 - name: "LY"
   description: "LY display manager"
   selected: false