nixos/grafana: add default value back to settings.server.socket

[SuperSandro2000]

Description of changes

Things done

• Built on platform(s)
  • x86_64-linux
  • aarch64-linux
  • x86_64-darwin
  • aarch64-darwin
• For non-Linux: Is sandbox = true set in nix.conf? (See Nix manual)
• Tested, as applicable:
  • NixOS test(s) (look inside nixos/tests)
  • and/or package tests
  • or, for functions and "core" functionality, tests in lib/tests or pkgs/test
  • made sure NixOS tests are linked to the relevant packages
• Tested compilation of all packages that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review rev HEAD". Note: all changes have to be committed, also see nixpkgs-review usage
• Tested basic functionality of all binary files (usually in ./result/bin/)
• 22.11 Release Notes (or backporting 22.05 Release notes)
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
  • (Release notes changes) Ran nixos/doc/manual/md-to-db.sh to update generated release notes
• Fits CONTRIBUTING.md.

[KFearsoff]

The reason I have removed the default value was because Grafana default for server.socket1 is /tmp/grafana.sock`, which I think is not particularly useful, so I felt that by removing the default value outright I give the user a need to choose.

That said, I don't know much about sockets and I don't feel strongly about that default, so LGTM.

[SuperSandro2000]

The default place for sockets in NixOS is /run/$name/$name.sock. Also if you use the socket in services.nginx.upstreams.<name>.servers then nginx will just crash on startup.

[KFearsoff]

Yeah, I also thought about the /run/$name/$name.sock convention when I saw the PR. The change makes sense. I don't have the necessary permissions to do so on Github, but I approve of the change.

[SuperSandro2000]

I think you should be able to leave a approval review but you can't merge it.