[centos 8] error during baking

During baking of Centos 8 image we got the following error:

```
caravan.googlecompute.opensource: TASK [hc_stack_install : install containerd, docker and docker-cli (RedHat)] ***
caravan.googlecompute.opensource: fatal: [127.0.0.1]: FAILED! => {"changed": false, "msg": "Failed to validate GPG signature for docker-ce-cli-1:20.10.8-3.el7.x86_64"}
```

Start by reproducing the CentOS 8 image bake and inspect the hc_stack_install task named in the error, especially package and GPG validation for docker-ce-cli. The work is done when the CentOS 8 image bake completes without the reported signature-validation failure.

Written by the indexing model from the issue text.