nixos/virtualbox: Adds more options to virtualbox-image.nix (#42699)

* nixos/virtualbox: Adds more options to virtualbox-image.nix

Previously you could only set the size of the disk.

This change adds the ability to change the amount of memory
that the image gets, along with the name / derivation name /
file name for the VM.

* Incorporates some review feedback

nixos/modules/virtualisation/virtualbox-image.nix

···
           The size of the VirtualBox base image in MiB.
         '';
       };
+      memorySize = mkOption {
+        type = types.int;
+        default = 1536;
+        description = ''
+          The amount of RAM the VirtualBox appliance can use in MiB.
+        '';
+      };
+      vmDerivationName = mkOption {
+        type = types.str;
+        default = "nixos-ova-${config.system.nixos.label}-${pkgs.stdenv.system}";
+        description = ''
+          The name of the derivation for the VirtualBox appliance.
+        '';
+      };
+      vmName = mkOption {
+        type = types.str;
+        default = "NixOS ${config.system.nixos.label} (${pkgs.stdenv.system})";
+        description = ''
+          The name of the VirtualBox appliance.
+        '';
+      };
+      vmFileName = mkOption {
+        type = types.str;
+        default = "nixos-${config.system.nixos.label}-${pkgs.stdenv.system}.ova";
+        description = ''
+          The file name of the VirtualBox appliance.
+        '';
+      };
     };
   };
 
   config = {
     system.build.virtualBoxOVA = import ../../lib/make-disk-image.nix {
-      name = "nixos-ova-${config.system.nixos.label}-${pkgs.stdenv.system}";
+      name = cfg.vmDerivationName;
 
       inherit pkgs lib config;
       partitionTableType = "legacy";
···
           VBoxManage internalcommands createrawvmdk -filename disk.vmdk -rawdisk $diskImage
 
           echo "creating VirtualBox VM..."
-          vmName="NixOS ${config.system.nixos.label} (${pkgs.stdenv.system})"
+          vmName="${cfg.vmName}";
           VBoxManage createvm --name "$vmName" --register \
             --ostype ${if pkgs.stdenv.system == "x86_64-linux" then "Linux26_64" else "Linux26"}
           VBoxManage modifyvm "$vmName" \
-            --memory 1536 --acpi on --vram 32 \
+            --memory ${toString cfg.memorySize} --acpi on --vram 32 \
             ${optionalString (pkgs.stdenv.system == "i686-linux") "--pae on"} \
             --nictype1 virtio --nic1 nat \
             --audiocontroller ac97 --audio alsa \
···
 
           echo "exporting VirtualBox VM..."
           mkdir -p $out
-          fn="$out/nixos-${config.system.nixos.label}-${pkgs.stdenv.system}.ova"
+          fn="$out/${cfg.vmFileName}"
           VBoxManage export "$vmName" --output "$fn"
 
           rm -v $diskImage