nixos/kata: pull in multi-user.target

Previously, due to setting `systemd.unit=kata-containers.target` on the kernel command line, we didn't pull in units that are `wantedBy=multi-user.target`. This breaks many assumptions of upstream software, including those of `nvidia-persistenced.service`, which was the first component that exhibited a hard breakage upon this unfulfilled assumption. This fixes these assumptions by pulling in `multi-user.target` through `kata-containers.target`.

packages/nixos/kata.nix

@@ -23,6 +23,7 @@ in
         "basic.target"
         "tmp.mount"
         "kata-agent.service"
+        "multi-user.target"
       ];
       wantedBy = [ "basic.target" ];
       wants = [
@@ -35,6 +36,7 @@ in
         "rescue.target"
       ];
       after = [
+        "multi-user.target"
         "basic.target"
         "rescue.service"
         "rescue.target"