ci: add integration testing via Nix

.github/workflows/integration.yml

@@ -0,0 +1,20 @@
+name: "Run integration tests"
+on:
+  pull_request:
+  push:
+jobs:
+  tests:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v3
+    - name: Enable KVM group perms
+        run: |
+            echo 'KERNEL=="kvm", GROUP="kvm", MODE="0666", OPTIONS+="static_node=kvm"' | sudo tee /etc/udev/rules.d/99-kvm4all.rules
+            sudo udevadm control --reload-rules
+            sudo udevadm trigger --name-match=kvm
+    - uses: cachix/install-nix-action@v20
+      with:
+        nix_path: nixpkgs=channel:nixos-unstable
+        extra_nix_config: "system-features = nixos-test benchmark big-parallel kvm"
+    - uses: DeterminateSystems/magic-nix-cache-action@v2
+    - run: nix flake check -L