Add CentOS 9 Stream mirror override

Hardcodes the CentOS 9 mirror for stream to get option working

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

@@ -63,6 +63,9 @@ goto boottype
 
 :bootos_images
 imgfree
+iseq ${osversion} 9-stream && set centos_mirror http://mirror.stream.centos.org || 
+iseq ${osversion} 9-stream && set dir ${osversion}/BaseOS/${os_arch}/os ||
+iseq ${osversion} 9-stream && set repo ${centos_mirror}/${dir} ||
 kernel ${centos_mirror}/${dir}/images/pxeboot/vmlinuz inst.repo=${repo} ${params} ${ipparam} {{ kernel_params }}
 initrd ${centos_mirror}/${dir}/images/pxeboot/initrd.img
 echo