nixos-generate-config: Set linuxPackages_latest when ISO boots latest kernel

nixos/modules/installer/cd-dvd/latest-kernel.nix

···
 {
   boot.kernelPackages = pkgs.linuxPackages_latest;
   boot.supportedFilesystems.zfs = false;
+  environment.etc."nixos-generate-config.conf".text = ''
+    [Defaults]
+    Kernel=latest
+  '';
 }

nixos/modules/installer/tools/manpages/nixos-generate-config.8

···
 .Op Fl -root Ar root
 .Op Fl -dir Ar dir
 .Op Fl -flake
+.Op Fl -kernel Ar <lts|latest>
 .
 .
 .
···
 instead of
 .Pa /etc/nixos Ns
 \&.
+.
+.It Fl -kernel Ar <lts|latest>
+Set the kernel in the generated configuration file.
 .
 .It Fl -force
 Overwrite

nixos/modules/installer/tools/nixos-generate-config.pl

···
 my $noFilesystems = 0;
 my $flake = 0;
 my $showHardwareConfig = 0;
+my $kernel = "lts";
 
 if (-e "/etc/nixos-generate-config.conf") {
     my $cfg = new Config::IniFiles -file => "/etc/nixos-generate-config.conf";
     $outDir = $cfg->val("Defaults", "Directory") // $outDir;
     $rootDir = $cfg->val("Defaults", "RootDirectory") // $rootDir;
+    $kernel = $cfg->val("Defaults", "Kernel") // $kernel;
 }
 
 for (my $n = 0; $n < scalar @ARGV; $n++) {
···
     elsif ($arg eq "--flake") {
         $flake = 1;
     }
+    elsif ($arg eq "--kernel") {
+        $n++;
+        $kernel = $ARGV[$n];
+        die "$0: ‘--kernel’ requires an argument\n" unless defined $kernel;
+    }
     else {
         die "$0: unrecognized argument ‘$arg’\n";
     }
···
 
 $rootDir =~ s/\/*$//; # remove trailing slashes
 $rootDir = File::Spec->rel2abs($rootDir); # resolve absolute path
+die "$0: invalid kernel: '$kernel'" unless $kernel eq "lts" || $kernel eq "latest";
 
 my @attrs = ();
 my @kernelModules = ();
···
   # boot.loader.efi.efiSysMountPoint = "/boot/efi";
   # Define on which hard drive you want to install Grub.
   # boot.loader.grub.device = "/dev/sda"; # or "nodev" for efi only
+EOF
+        }
+
+        if ($kernel eq "latest") {
+            $bootLoaderConfig .= <<EOF;
+
+  # Use latest kernel.
+  boot.kernelPackages = pkgs.linuxPackages_latest;
 EOF
         }
 

nixos/modules/installer/tools/tools.nix

···
     name = "nixos-generate-config";
     src = ./nixos-generate-config.pl;
     replacements = {
-      perl = "${pkgs.perl.withPackages (p: [ p.FileSlurp ])}/bin/perl";
+      perl = "${
+        pkgs.perl.withPackages (p: [
+          p.FileSlurp
+          p.ConfigIniFiles
+        ])
+      }/bin/perl";
       hostPlatformSystem = pkgs.stdenv.hostPlatform.system;
       detectvirt = "${config.systemd.package}/bin/systemd-detect-virt";
       btrfs = "${pkgs.btrfs-progs}/bin/btrfs";