Add pipeline to publish ghcr multi-arch image (#2268)

Refactor operator image build process
Add a pipeline to build and publish arm64/amd64 image in ghcr on every
pushed tag

docker/Dockerfile

@@ -1,11 +1,24 @@
-FROM registry.opensource.zalan.do/library/alpine-3.15:latest
+ARG BASE_IMAGE=registry.opensource.zalan.do/library/alpine-3.15:latest
+ARG VERSION=latest
+
+FROM ubuntu:20.04 as builder
+
+ARG VERSION
+
+COPY  . /go/src/github.com/zalando/postgres-operator
+WORKDIR /go/src/github.com/zalando/postgres-operator
+
+ENV OPERATOR_LDFLAGS="-X=main.version=${VERSION}"
+RUN bash docker/build_operator.sh
+
+FROM ${BASE_IMAGE}
 LABEL maintainer="Team ACID @ Zalando <team-acid@zalando.de>"
 
 # We need root certificates to deal with teams api over https
 RUN apk --no-cache add curl
 RUN apk --no-cache add ca-certificates
 
-COPY build/* /
+COPY --from=builder /go/src/github.com/zalando/postgres-operator/build/* /
 
 RUN addgroup -g 1000 pgo
 RUN adduser -D -u 1000 -G pgo -g 'Postgres Operator' pgo

docker/build_operator.sh

@@ -0,0 +1,31 @@
+#!/bin/bash
+
+export DEBIAN_FRONTEND=noninteractive
+
+arch=$(dpkg --print-architecture)
+
+set -ex
+
+# Install dependencies
+
+apt-get update
+apt-get install -y wget
+
+(
+    cd /tmp
+    wget -q "https://storage.googleapis.com/golang/go1.18.9.linux-${arch}.tar.gz" -O go.tar.gz
+    tar -xf go.tar.gz
+    mv go /usr/local
+    ln -s /usr/local/go/bin/go /usr/bin/go
+    go version
+)
+
+# Build
+
+export PATH="$PATH:$HOME/go/bin"
+export GOPATH="$HOME/go"
+mkdir -p build
+cp scm-source.json build/
+
+GO111MODULE=on go mod vendor
+CGO_ENABLED=0 go build -o build/postgres-operator -v -ldflags "$OPERATOR_LDFLAGS" cmd/main.go