Add the readme symlink task back as an interim solution

We have redirect loops only in the 14.1 branch. I suspect it's due to https://gitlab.com/gitlab-org/gitlab-docs/-/blob/58aa283e315712a81a406d14bf07483112b6e7e8/scripts/normalize-links.sh#L89

That means that when we removed the new task in !1925 (merged), it started using the old automated code, which just added a symlink for every README.md found. By putting in the raketask again, but with an empty file, the old code won't be triggered, and the new code will run but won't find anything to symlink, and will just stop without adding any symlinks.

Let's merge to main first, for future branches (14.2), then port to 14.1, while we work on a better solution.