[DNS] Dune developer preview url

[maiste]

Hi :wave: We are on our way to publish the Dune Developer Preview to the public (with Dune package management as a notorious feature). Currently, the website is host under https://dune.ci.dev and https://download.dune.ci.dev (and developed at https://github.com/tarides/dune-binary-distribution). However, as it will be on the https://ocaml.org website (Draft PR: https://github.com/ocaml/ocaml.org/pull/2706), we would like to add a new subdomain for this under the ocaml.org domain.

Our suggestion would be to have:

• dune.ocaml.org to replace dune.ci.dev
• get.ocaml.org to replace download.dune.ci.dev

The DNS would be the following:

dune.ocaml.org CNAME tarides.github.io.
get.ocaml.org A 51.159.152.205
get.ocaml.org AAAA 2001:bc8:1202:dc31::1

The CNAME is temporary, as we host the website on GitHub for the development period.