opam.ocaml.org migration to v3.ocaml.org

[avsm]

Once #19 is completed and the new opam.ocaml.org servers are stable, we need to start on merging opam.ocaml.org and ocaml.org/p and finishing the consolidation. Some low hanging fruits first:

• [ ] ocaml.org's SEO is terrible at present since there isn't a sitemap.xml generated. (tracked in ocaml/ocaml.org#754)
• [ ] the opam.ocaml.org opam2web could be modified easily to add a link to the ocaml.org/p version, which has the documentation. Right now there's no mention of it at all. /cc @dra27 @rjbou
• [x] the ocaml.org package page isn't at parity in terms of the information it displays vs opam.ocaml.org. The two missing fields are package conflicts, and an edit link to the opam file. (tracked in ocaml/ocaml.org#755 and ocaml/ocaml.org#756)

Once that's done, we could do with a plan for how to migrate.

• [ ] all old links to opam.ocaml.org must continue to work, but a redirect is fine.
• [ ] integrate the opam documentation and manuals directly into ocaml.org.
• [x] redirect the platform blog over to ocaml.org. Already being worked on in https://github.com/ocaml/ocaml.org/issues/691

[tmattio]

@avsm we merged patches to address the parity with opam.ocaml.org: https://github.com/ocaml/ocaml.org/pull/764 and https://github.com/ocaml/ocaml.org/pull/762.

The sitemap might be a bit more involved, but we'll have a look.

[tmattio]

Status update: as far as I can tell, the only remaining blocker to retire opam.ocaml.org is to move the opam documentation to ocaml.org. We're currently working on the learn area and improving the documentation and we'll migrate the opam.ocaml.org documentation as part of this.

We've worked on the sitemap to improve SEO, but I don't think this is blocking the migration (ocaml.org SEO should have improved since January)

When we have this, I think we're ready to put redirections from opam.ocaml.org to ocaml.org/p

[sabine]

I posted an issue at https://github.com/ocaml-opam/opam2web/issues/227 to give people some warning that opam2web is going to retire soon-ish.

Also, I am inclined to host only the opam 2 documentation on ocaml.org until odoc generates manuals - then, we can move the opam docs into an opam package and show the documentation for all versions on ocaml.org.

Do we need to host the man pages of opam (my current draft of a patch doesn't)? If so, I'll host them on ocaml.org as well, but if we can omit those, it will place less complexity on the ocaml.org codebase.

Note: The legacy opam 1.1 and 1.2 documentation is still available under the corresponding tag in the https://github.com/ocaml/opam repository in the doc folder.