Allow adding custom options to individual vms

lib/config/custom-build-vm.nix

@@ -1,5 +1,13 @@
-{ config, lib, options, pkgs, ... }: {
-  options = {};
+{ config, lib, options, pkgs, ... }:
+  let
+    vmOptions = { };
+  in {
+    options = {
+      virtualisation = {
+        vmVariant = vmOptions;
+        vmVariantWithBootLoader = vmOptions;
+      };
+    };
 
     config = {
       # Replace native `qemu` with `remote-viewer`
@@ -41,26 +49,5 @@
                       paths = [ wrapped ];
                     });
         };
-
-    virtualisation =
-      let vmConfig = {
-        boot.loader.efi.efiSysMountPoint = lib.mkForce "/boot";
-
-        virtualisation = {
-          qemu.options = [
-            "-display sdl"
-          ];
-
-          sharedDirectories = {
-            hostKeys = {
-              source = "/etc/ssh";
-              target = "/etc/ssh";
-            };
-          };
-        };
-      };
-      in {
-        vmVariantWithBootLoader = vmConfig;
-      };
     };
   }