Introduce multiarch docker image build

.github/workflows/build-release.yaml

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+on:
+  push:
+    tags:
+      - '*'
+  release:
+    types:
+      - created
+name: Build release
+jobs:
+  docker:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v2
+      - name: Get the version
+        id: get_version
+        run: echo ::set-output name=VERSION::${GITHUB_REF/refs\/tags\//}
+      - uses: frabert/replace-string-action@master
+        id: formatted_version
+        with:
+          pattern: '[v]*(.*)$'
+          string: "${{ steps.get_version.outputs.VERSION }}"
+          replace-with: '$1'
+          flags: 'g'
+      - name: Set up QEMU
+        uses: docker/setup-qemu-action@v1
+      - name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v1
+      - name: Login to Docker Registry
+        uses: docker/login-action@v1 
+        with:
+          username: ${{ secrets.DOCKER_USERNAME }}
+          password: ${{ secrets.DOCKER_TOKEN }}
+          registry: ${{ secrets.DOCKER_REGISTRY }}
+      - name: Build and push
+        uses: docker/build-push-action@v2
+        with:
+          context: .
+          file: Dockerfile.multiarch
+          platforms: linux/amd64,linux/arm64
+          push: true
+          tags: ${{ secrets.DOCKER_REGISTRY }}/${{ secrets.DOCKER_ORGANIZATION }}/kiam:${{ steps.formatted_version.outputs.replaced }}

Dockerfile.multiarch

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+FROM golang:1.13.8 as build
+ENV GO111MODULE=on
+
+WORKDIR /workspace
+# Copy the Go Modules manifests
+COPY go.mod go.mod
+COPY go.sum go.sum
+# cache deps before building and copying source so that we don't need to re-download as much
+# and so that source changes don't invalidate our downloaded layer
+RUN go mod download
+
+COPY cmd/ cmd/
+COPY pkg/ pkg/
+COPY proto/ proto/
+COPY Makefile Makefile
+
+RUN CGO_ENABLED=0 go build -o bin/kiam cmd/kiam/*.go
+
+FROM alpine:3.11
+RUN apk --no-cache add iptables
+COPY --from=build /workspace/bin/kiam /kiam
+CMD []