update nixos menu to ingest all of their external tags and boot off of their IPXE files

roles/netbootxyz/templates/menu/nixos.ipxe.j2

@@ -6,20 +6,13 @@
 set os {{ releases.nixos.name }}
 menu ${os}
 item --gap Official Releases
-{% for key, value in endpoints.items() | sort %}
-{% if value.os == "nixos" %}
-item {{ value.version }} ${space} ${os} {{ value.version }}
-{% endif %}
+{% for item in releases.nixos.versions %}
+item {{ item.code_name }} ${space} ${os} {{ item.name }}
 {% endfor %}
 choose version || goto nixos_exit
 
-{% for key, value in endpoints.items() | sort %}
-{% if value.os == "nixos" %}
-iseq ${version} {{ value.version }} && set link ${live_endpoint}{{ value.path }}netboot.ipxe ||
-{% endif %}
-{% endfor %}
 imgfree
-chain ${link}
+chain https://github.com/nix-community/nixos-images/releases/download/${version}/netboot-x86_64-linux.ipxe
 goto nixos_exit
 
 :nixos_exit