Registry config reference is moved

[hoerup]

https://goharbor.io/docs/2.9.0/install-config/configure-yml-file/#backend

The link for registry storage config should now point to https://distribution.github.io/distribution/storage-drivers/

[sergioarmgpl]

I can work on this, where I have to update this link? I saw just the "Distribution Configuration Reference with this link https://distribution.github.io/distribution/about/configuration/ @hoerup

[Vad1mo]

@hoerup @sergioarmgpl, we normally don't change the history or the old documentation, and leave it more as is. However we should update the new documentation instead, if not done yet.