Update nixdoc in Nixpkgs

[fricklerhandwerk]

We need not only to bump the package, but to also update the way it's used to produce Nixpkgs documentation, since the new version produces CommonMark, not DocBook.

https://github.com/NixOS/nixpkgs/tree/0bc15605ceb122f6975116015e2fbd153102c7a0/doc/doc-support/lib-function-docs.nix#L11

[pennae]

wip at https://github.com/pennae/nixpkgs/tree/nixpkgs-manual-nrd, pending nix-community/nixdoc#35 being merged

[asymmetric]

@pennae do you want to take ownership of this? IIUC you're reworking the way the nixpkgs manual is produced, so it makes no sense for me right now to integrate nixdoc 2 into the current Makefile-based workflow.

[nixos-discourse]

This issue has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/2023-04-11-documentation-team-meeting-notes-40/27261/1

[pennae]

done in #239636