If container engine enabled, set oci backand accordingly

modules/virtualisation/docker.nix

@@ -21,6 +21,9 @@ in
           setSocketVariable = true;
         };
       };
+
+      oci-containers.backend = "podman";
+
     };
   };
 

modules/virtualisation/podman.nix

@@ -13,11 +13,13 @@ in
   };
 
   config = lib.mkIf cfg.enable {
-    virtualisation.podman = {
-      enable = true;
+    virtualisation = {
 
-      # Depending on the host filesystem
-      # extraPackages = [ pkgs.zfs ];
+      podman = {
+        enable = true;
+      };
+
+      oci-containers.backend = "podman";
     };
 
     # Depending on the host filesystem