offline install using containerd runtime (#8254)

install containerd on centos need to binary download it 

but offline.yml has no that value

binary download url default in

roles/download/defaults/main.yml:runc_download_url: "https://github.com/opencontainers/runc/releases/download/{{ runc_version }}/runc.{{ image_arch }}"
roles/download/defaults/main.yml:containerd_download_url: "https://github.com/containerd/containerd/releases/download/v{{ containerd_version }}/containerd-{{ containerd_version }}-linux-{{ image_arch }}.tar.gz"

if i use default offlie.yml, it's error from task download files

because runc,containerd down url is none offline

i want fix this 

just add 2 new line

inventory/sample/group_vars/all/offline.yml

@@ -49,6 +49,10 @@
 # crio_download_base: "download.opensuse.org/repositories/devel:kubic:libcontainers:stable"
 # crio_download_crio: "http://{{ crio_download_base }}:/cri-o:/"
 
+# [Optional] runc,containerd: only if you set container_runtime: containerd
+# runc_download_url: "{{ files_repo }}/{{ runc_version }}/runc.{{ image_arch }}"
+# containerd_download_url: "{{ files_repo }}/containerd/v{{ containerd_version }}/containerd-{{ containerd_version }}-linux-{{ image_arch }}.tar.gz"
+
 ## CentOS/Redhat/AlmaLinux
 ### For EL7, base and extras repo must be available, for EL8, baseos and appstream
 ### By default we enable those repo automatically