Motivation for this change

Add the sqldiff utility (https://sqlite.org/sqldiff.html)

NOTE: I also extracted the version.nix to share it across sql-analyzer, sqlite and sqldiff and removed the manual assert

I'm a bit unsure about the building process, we could also build sqldiff together with sqlite, but for that we would have to use a different source than the one that is currently used... I saw that the sql-analyzer does it in the way that I used for sqldiff

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.