Add initial setup for Central DNS and PXE services using dnsmasq

- Created README.md for Central setup documentation.
- Added dnsmasq configuration files and scripts for setting up DNS and PXE booting.
- Implemented nginx configuration to serve PXE boot assets.
- Developed setup.sh script to automate installation and configuration of dnsmasq and nginx.
- Removed outdated dnsmasq setup guide from documentation.

central-setup/dnsmasq/bare-metal.yaml

@@ -0,0 +1,7 @@
+customization:
+  extraKernelArgs:
+    - net.ifnames=0
+  systemExtensions:
+    officialExtensions:
+      - siderolabs/gvisor
+      - siderolabs/intel-ucode