Add zombienet integration (polkadot-fellows#307)

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Hi 👋 , this pr add a very small smoke test as PoC of using
[zombienet-sdk](https://github.com/paritytech/zombienet-sdk) with the
_runtimes_ repo. The idea is to explore the integration and add more
assertions (metrics, logs, etc) and complex scenarios in the future
(e.g: test upgrades, mix node's versions, etc).

This test use a set of _env vars_ that allow you to specify the images
and the provider to use:
`POLKADOT_IMAGE` (_default_: docker.io/parity/polkadot:latest)
`CUMULUS_IMAGE` (_default_: docker.io/parity/polkadot-parachain:latest)
`ZOMBIE_PROVIDER`(_default_: Docker)

And needs to have the `chain-spec-generator` binary as part of your
`PATH`, any feedback is welcome :)

--- 
Also worth notice that the `chain-spec-generator` tool is compiling all
the runtimes, and would be good to only compile the needed ones
(polkadot in this case), we can add some feature-gate logic or we can
also move _ presets_ to runtimes (ping @michalkucharczyk ).

Thanks!

---------

Co-authored-by: Bastian Köcher <git@kchr.de>

.github/workflows/test.yml

@@ -189,3 +189,54 @@ jobs:
         env:
           RUSTFLAGS: "-C debug-assertions -D warnings"
           SKIP_WASM_BUILD: 1
+
+  zombienet-smoke:
+    needs: [build-chain-spec-generator]
+    runs-on: ubuntu-latest
+    steps:
+      - name: Cancel previous runs
+        uses: styfle/cancel-workflow-action@b173b6ec0100793626c2d9e6b90435061f4fc3e5 # v0.11.0
+        with:
+          access_token: ${{ github.token }}
+
+      - name: Install updates and protobuf-compiler
+        run: sudo apt update && sudo apt install --assume-yes cmake protobuf-compiler
+
+      - name: Free space on the runner
+        run: |
+          df -h
+          sudo apt -y autoremove --purge
+          sudo apt -y autoclean
+          sudo rm -rf /usr/share/dotnet
+          sudo rm -rf /opt/ghc
+          sudo rm -rf "/usr/local/share/boost"
+          sudo rm -rf "$AGENT_TOOLSDIRECTORY"
+          df -h
+
+      - name: Checkout
+        uses: actions/checkout@v3
+
+      - name: Set rust version via common env file
+        run: cat .github/env >> $GITHUB_ENV
+
+      - name: Install stable toolchain
+        run: |
+          rustup install $RUST_STABLE_VERSION
+          rustup default $RUST_STABLE_VERSION
+          rustup target add wasm32-unknown-unknown
+          rustup component add rust-src
+
+      - name: Fetch cache
+        uses: Swatinem/rust-cache@a95ba195448af2da9b00fb742d14ffaaf3c21f43 # v2.7.0
+        with:
+          shared-key: "fellowship-cache-integration-tests"
+
+      - name: Build
+        run: |
+          cargo build -p chain-spec-generator --features fast-runtime --release --locked
+
+      - name: Zombienet smoke test
+        timeout-minutes: 20
+        run: |
+          export PATH=$(pwd)/target/release:$PATH
+          cargo test --manifest-path integration-tests/zombienet/Cargo.toml