nix --version only shows version of the CLI not of the demon

[NobbZ]

Is your feature request related to a problem? Please describe.

When I re-installed my system the last time, I used nix-shell -p nixUnstable to enter a shell with flakes enabled.

nixos-rebuild exited with errors about --extra-experimental-features beeing unknown.

nix --version told me, that I was on a recent nix version (2.4pre somewhen from beginning of August).

As that didn't work properly, I tried nix shell github:nixos/nix to get a nix from now, and I got the same error as before.

After a lot of trial and error I realized, that the demon still was running nix 2.3 and assumed that the error might be coming from the demon.

Describe the solution you'd like

nix --version should show not only the version of the nix CLI itself, but also of the demon it is connecting to (if it is using a demon).

Describe alternatives you've considered

There is no real alternative to this. But displaying client and server version separately is quite common in applications that are split in client and server.

[NobbZ]

As #5952 got fixed by #5991, can we include the demon version in the nix --version output as well?

That is a lot more intuitive than nix store ping.