feat(deck): Add service to return to gaming mode

Fixes users not being to switch to gaming mode when they have desktop autologin toggled
and should allow users to start gaming mode immediately after Steam has been updated
instead of having to reboot after setup (although this should be done regardless)

system_files/deck/shared/usr/bin/return-to-gamemode

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+
+source /etc/default/bazzite
+
+USER=$(id -nu 1000)
+
+# SteamOS autologin SDDM config
+AUTOLOGIN_CONF='/etc/sddm.conf.d/zz-steamos-autologin.conf'
+
+# Configure autologin if Steam has been updated
+if [[ -f /var/home/$USER/.local/share/Steam/ubuntu12_32/steamui.so ]]; then
+  {
+    echo "[Autologin]"
+    echo "Session=gamescope-session.desktop"
+  } > "$AUTOLOGIN_CONF"
+fi
+
+if [[ $BASE_IMAGE_NAME = "kinoite" ]]; then
+  sudo -Eu $USER qdbus org.kde.Shutdown /Shutdown org.kde.Shutdown.logout
+elif [[ $BASE_IMAGE_NAME = "silverblue" ]]; then
+  sudo -Eu $USER gnome-session-quit --logout --no-prompt
+fi

system_files/deck/shared/usr/etc/polkit-1/rules.d/return-to-gamemode.rules

@@ -0,0 +1,8 @@
+polkit.addRule(function(action, subject) {
+    if (subject.isInGroup("wheel") &&
+        action.id == "org.freedesktop.systemd1.manage-units" &&
+        action.lookup("unit") == "return-to-gamemode.service")
+    {
+        return polkit.Result.YES;
+    }
+})

system_files/deck/shared/usr/lib/systemd/system/return-to-gamemode.service

@@ -0,0 +1,6 @@
+[Unit]
+Description=Return to Gaming Mode
+
+[Service]
+Type=oneshot
+ExecStart=/usr/bin/return-to-gamemode