feat: add advanced options for Fennix boot menu in grub.cfg

Signed-off-by: EnderIce2 <enderice2@protonmail.com>

tools/grub.cfg

@@ -14,6 +14,34 @@ menuentry "Fennix" {
 	boot
 }
 
+submenu "Advanced Options..." {
+	menuentry "Fennix (Linux Subsystem)" {
+		load_video
+		clear
+		echo "Loading kernel in Linux Subsystem mode"
+		multiboot2 /fennix.elf --init=/bin/init --linux=true
+		echo "Loading rootfs"
+		module2 /rootfs.tar rootfs
+		echo "Booting..."
+		boot
+	}
+
+	menuentry "Fennix (Recovery)" {
+		load_video
+		clear
+		echo "Loading kernel in recovery mode"
+		multiboot2 /fennix.elf
+		echo "Loading rootfs"
+		module2 /rootfs.tar rootfs
+		echo "Booting..."
+		boot
+	}
+}
+
+menuentry ' ' {
+	exit 1
+}
+
 menuentry 'Boot from next volume' {
 	exit 1
 }