manual: list experimental features

[fricklerhandwerk]

Problem

The manual only shows the configuration option experimental-features, but does not list which exist.

Checklist

• checked latest Nix manual (source)
• checked open documentation issues and pull requests for possible duplicates

Proposal

Include the list in the documentation for the configuration option experimental-features.

The list is maintained in experimental-features.cc.

Configuration options are compiled to markdown in the Make rule for conf-file.md by passing the output of nix show-config to generate-options.nix.

[aameen-tulip]

I think this is a great idea. Currently I have to grep the repo to find them.

[fricklerhandwerk]

Closed by #7798

[nixos-discourse]

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

https://discourse.nixos.org/t/2023-04-17-nix-team-meeting-minutes-49/27379/1