Add PXE boot configuration and scripts

* **PXE boot configuration**: Add `dnsmasq.conf` to configure PXE boot, set TFTP root directory, and configure DHCP options.
* **PXE bootloader configuration**: Add `pxelinux.cfg/default` to configure the PXE bootloader and set the bootloader to point to the macOS KVM kernel/initrd.
* **Serve PXE boot files**: Add `serve_pxe.sh` script to serve `pxelinux.0`, `vmlinuz`, and `initrd` via TFTP using `dnsmasq`.
* **Retrieve internal IP**: Add `get_internal_ip.sh` script to retrieve the internal IP address of the Codespace.
* **Update boot script**: Modify `boot-macOS-headless.sh` to use the PXE boot files from the `netboot` directory and add a network boot option to the QEMU command.

boot-macOS-headless.sh

@@ -67,6 +67,8 @@ args=(
   -device vmware-svga
   -display none
   -vnc 0.0.0.0:1,password=on -k en-us
+  -netdev user,id=pxenet0,tftp=netboot/tftpboot,bootfile=pxelinux.0
+  -device e1000,netdev=pxenet0
 )
 
 qemu-system-x86_64 "${args[@]}"

netboot/dnsmasq.conf

@@ -0,0 +1,10 @@
+# Configuration for dnsmasq to support PXE boot
+
+# Set the TFTP root directory
+enable-tftp
+tftp-root=/tftpboot
+
+# Configure DHCP options for PXE boot
+dhcp-range=192.168.1.100,192.168.1.200,12h
+dhcp-boot=pxelinux.0
+pxe-service=x86PC, "Install macOS", pxelinux

netboot/get_internal_ip.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+# Script to retrieve the internal IP address of the Codespace
+
+hostname -I

netboot/pxelinux.cfg/default

@@ -0,0 +1,4 @@
+DEFAULT macOS
+LABEL macOS
+  KERNEL vmlinuz
+  APPEND initrd=initrd.img

netboot/serve_pxe.sh

@@ -0,0 +1,24 @@
+#!/bin/bash
+
+# Serve pxelinux.0, vmlinuz, and initrd via TFTP using dnsmasq
+
+# Ensure dnsmasq is installed
+if ! command -v dnsmasq &> /dev/null
+then
+    echo "dnsmasq could not be found, please install it."
+    exit
+fi
+
+# Create tftpboot directory if it doesn't exist
+TFTPBOOT_DIR="tftpboot"
+if [ ! -d "$TFTPBOOT_DIR" ]; then
+    mkdir -p "$TFTPBOOT_DIR"
+fi
+
+# Copy necessary files to tftpboot directory
+cp pxelinux.0 "$TFTPBOOT_DIR/"
+cp vmlinuz "$TFTPBOOT_DIR/"
+cp initrd.img "$TFTPBOOT_DIR/"
+
+# Start dnsmasq to serve PXE boot files
+dnsmasq --conf-file=netboot/dnsmasq.conf