N1C, when adding instances to a CSG

[mjang]

Describe the bug

Discussion in Slack. Change as suggested by @sylwang

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Yes, I think we can add clarifications to the section for https://docs.nginx.com/nginx-one/how-to/config-sync-groups/manage-config-sync-groups/#add-a-new-instance-to-a-config-sync-group, to include the fact that a publication should be automatically issued first to sync the instance. They should watch out for any publication failure on that instance, and would need to fix the issue. By looking at the instance details in the console, they should be able to view the publication failure. Once they resolve it, they can publish the current config on the CSG, and retry syncing the instance.

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