add e2e github action

.github/workflows/e2e.yml

@@ -0,0 +1,42 @@
+name: End-to-end interoperability testing
+
+on: [push, pull_request]
+
+jobs:
+  tests:
+    name: Tests
+
+    strategy:
+      fail-fast: false
+      matrix:
+        ocaml-version: ["4.14.2"]
+        operating-system: [ubuntu-latest]
+
+    runs-on: ${{ matrix.operating-system }}
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Use OCaml ${{ matrix.ocaml-version }}
+        uses: ocaml/setup-ocaml@v2
+        with:
+          ocaml-compiler: ${{ matrix.ocaml-version }}
+
+      - name: Install openvpn
+        run: apt install openvpn
+
+      - name: Install dependencies
+        run: opam install --deps-only -t .
+
+      - name: Build
+        run: opam exec -- dune build --instrument-with bisect-ppx
+
+      - name: Testing
+        run: |
+          opam exec -- dune runtest --instrument-with bisect-ppx
+          opam exec -- dune exec bench/bench_engine.exe
+          ip tuntap add mode tun e22-test
+          cd tests/e2e && ./test-server.sh e2e-test
+          cd tests/e2e && ./test-client.sh e2e-test
+          ./coverage.sh