Update docs for v1.6.0 RC2

[carlisia]

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Fixes #(issue)

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[ashish-amarnath]

upgrade-to-1.6.md references the rc-1 release, that needs to be changed to rc-2

[ashish-amarnath]

Thanks for making the changes!

[zubron]

I was looking through the previous PR for the docs upgrade and noticed this comment: #3659 (review).

It's correct that we don't create a new version of the docs for each patch release, but our site and scripts are set up to assume that the full version string is used for pre-release versions: https://github.com/vmware-tanzu/velero/blob/main/hack/release-tools/gen-docs.sh#L37-L39.
Using v1.6 as the version for an RC means that the header on the docs looks like it's an out of date version: https://deploy-preview-3660--velero.netlify.app/docs/v1.6/ due to this.

It's not that I feel particularly strongly about this, it's just that using the GA version string for a pre-release doesn't match what our docs and scripts include, so we should either update the docs and scripts, or use the full version string.

[ashish-amarnath]

That makes sense. Thanks for that info @zubron
I agree that we don't want our pre-release to get a GA version string in the docs.
Sorry I missed that @carlisia.

[carlisia]

Haha I didn't trust the docs. The ones I wrote.

Closing this and opening a new one.