Backport old deprecation nfs

What does this MR do and why?

we introduced a new deprecation process https://about.gitlab.com/handbook/marketing/blog/release-posts/#deprecations

And need to backport in the older (14.0+) deprecations to match the new process

this one was announced in 14-0 https://about.gitlab.com/releases/2021/06/22/gitlab-14-0-released/#nfs-for-git-repository-storage-deprecated

https://gitlab.com/gitlab-com/www-gitlab-com/-/blob/master/data/release_posts/14_0/dep-gitaly-nfs.yml

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