fix: add branding packages to Default group, populate services-artix, create online grubcfg

- Add antergos-release, antergos-next-keyring, antergos-wallpapers to
  Default netinstall group (both global and online) so installed system
  keeps Antergos branding instead of appearing as plain Artix
- Populate services-artix.conf (both online + offline) with service names
  so SDDM, NetworkManager, dbus, etc. are enabled after install (fixes
  boot-to-TTY issue)
- Create grubcfg.conf for online mode with GRUB_THEME default so
  antergos-grub-theme is actually applied by grub-mkconfig

iso-profiles/antergos/live-overlay/etc/calamares-online/modules/grubcfg.conf

@@ -0,0 +1,21 @@
+# SPDX-FileCopyrightText: no
+# SPDX-License-Identifier: CC0-1.0
+---
+# Create /etc/default/grub from scratch.
+overwrite: true
+
+prefer_grub_d: false
+
+keep_distributor: false
+
+kernel_params: [ "quiet", "splash" ]
+
+defaults:
+    GRUB_TIMEOUT: 5
+    GRUB_DEFAULT: "saved"
+    GRUB_DISABLE_SUBMENU: true
+    GRUB_TERMINAL_OUTPUT: "console"
+    GRUB_DISABLE_RECOVERY: true
+    GRUB_THEME: "/usr/share/grub/themes/antergos/theme.txt"
+
+always_use_defaults: false