command-not-found: add NIX_AUTO_RUN

nixos/modules/programs/command-not-found/command-not-found.nix

···
     isExecutable = true;
     inherit (pkgs) perl;
     perlFlags = concatStrings (map (path: "-I ${path}/lib/perl5/site_perl ")
-      [ pkgs.perlPackages.DBI pkgs.perlPackages.DBDSQLite ]);
+      [ pkgs.perlPackages.DBI pkgs.perlPackages.DBDSQLite pkgs.perlPackages.StringShellQuote ]);
   };
 
 in

nixos/modules/programs/command-not-found/command-not-found.pl

···
 use strict;
 use DBI;
 use DBD::SQLite;
+use String::ShellQuote;
 use Config;
 
 my $program = $ARGV[0];
···
 EOF
         ;
         exit 126 if system("nix-env", "-iA", "nixos.$package") == 0;
+    } elsif ($ENV{"NIX_AUTO_RUN"} // "") {
+        exec("nix-shell", "-p", $package, "--run", shell_quote("exec", @ARGV));
     } else {
         print STDERR <<EOF;
 The program ‘$program’ is currently not installed. You can install it by typing: