Initial seed deployment docs update

[gc-nathanh]

Following https://stackhpc-kayobe-config.readthedocs.io/en/stackhpc-2023.1/configuration/release-train.html#syncing-content to deploy Pulp before Bifrost, I hit an error

TASK [deploy-containers : Login to docker registry] *********************************************************************************************************************************************************************************************************
Tuesday 19 March 2024  08:38:59 +0000 (0:00:01.467)       0:00:01.500 *********
fatal: [seedvm]: FAILED! => changed=false
  msg: 'Logging into 192.168.1.20:80 for user admin failed - 500 Server Error for http+docker://localhost/v1.44/auth: Internal Server Error ("Get "http://192.168.1.20:80/v2/": dial tcp 192.168.1.20:80: connect: connection refused")'

The extra var disables the task via

  when:
   - deploy_containers_registry_attempt_login | bool

[gc-nathanh]

FAO @bbezak - it almost worked as documented, but completed with -e deploy_containers_registry_attempt_login=false