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