Include multiarch buld into Docker

[maltegrosse]

Would be nice to have build process included into the Dockerfile, for example:

ARG ARCH=amd64

# build stage
FROM golang:1.13 AS builder
RUN mkdir -p /go/src/app
WORKDIR /go/src/app
COPY . ./
RUN go mod download
RUN go mod verify
RUN CGO_ENABLED=0 GOOS=linux GOARCH=$ARCH go build -a -o /app .


# final stage
FROM alpine:latest
RUN apk --no-cache add ca-certificates
COPY --from=builder /app ./
RUN chmod +x ./app
ENTRYPOINT ["./app"]
EXPOSE 80

[joonas-fi]

Our build tool actually already supported Docker multi-arch builds. I enabled the flag and now there's a Docker Hub image with multiple architectures