Try to build docker on ci

.dockerignore

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+**/target

.github/workflows/build-docker.yml

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+name: Build docker image
+
+on:
+  push:
+    branches:
+      - main
+      - master
+      - rzadp/test-dockerfile
+
+
+jobs:
+  ci:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+
+      # We've run into out-of-disk error when compiling Polkadot in the next step, so we free up some space this way.
+      - name: Free Disk Space (Ubuntu)
+        uses: jlumbroso/free-disk-space@54081f138730dfa15788a46383842cd2f914a1be # 1.3.1
+        with:
+          android: true # This alone is a 12 GB save.
+          # We disable the rest because it caused some problems. (they're enabled by default)
+          # The Android removal is enough.
+          dotnet: false
+          haskell: false
+          large-packages: false
+          swap-storage: false
+
+      - name: Build the docker image
+        run: docker build . -t polkadot-sdk-minimal-template

Dockerfile

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+# This is the build stage for Polkadot. Here we create the binary in a temporary image.
+FROM docker.io/paritytech/ci-linux:production as builder
+
+WORKDIR /polkadot
+COPY . /polkadot
+
+RUN cargo build --locked --release
+
+# This is the 2nd stage: a very small image where we copy the Polkadot binary."
+FROM docker.io/parity/base-bin:latest
+
+LABEL description="Multistage Docker image for Polkadot: a platform for web3"
+
+COPY --from=builder /polkadot/target/release/polkadot /usr/local/bin
+
+RUN useradd -m -u 1000 -U -s /bin/sh -d /polkadot polkadot && \
+	mkdir -p /data /polkadot/.local/share && \
+	chown -R polkadot:polkadot /data && \
+	ln -s /data /polkadot/.local/share/polkadot && \
+# unclutter and minimize the attack surface
+	rm -rf /usr/bin /usr/sbin && \
+# check if executable works in this container
+	/usr/local/bin/polkadot --version
+
+USER polkadot
+
+EXPOSE 30333 9933 9944 9615
+VOLUME ["/data"]
+
+ENTRYPOINT ["/usr/local/bin/polkadot"]