Add preliminary Debian 11 (bullseye) support (#7853)

- Use python3-apt instead because python-apt was removed in Debian 11
- Add gnupg (fix "container-engine/containerd : ensure containerd repository public key is installed" task failed)
- Remove aufs-tools

Signed-off-by: rtsp <git@rtsp.us>

roles/kubernetes/preinstall/vars/debian-11.yml

@@ -0,0 +1,7 @@
+---
+required_pkgs:
+  - python3-apt
+  - gnupg
+  - apt-transport-https
+  - software-properties-common
+  - conntrack