Initial multi-arch image commit (#86)

Adding multi-arch image support for `arm64` and `amd64`. This uses dockers new `buildx` feature, to enable further architectures more work will be required to update the `runner/Dockerfile` file to pull architecture-specific releases.

The Makefile targets really should only be used for local testing and not for release, additional work to appropriately tag the release images may need to be added but for now, I've not added that logic.

Fixes: #86 

Signed-off-by: Michael Fornaro <20387402+xUnholy@users.noreply.github.com>

Dockerfile

@@ -1,28 +1,37 @@
 # Build the manager binary
 FROM golang:1.13 as builder
 
+ARG TARGETPLATFORM
+
 WORKDIR /workspace
+
+ENV GO111MODULE=on \
+  CGO_ENABLED=0
+
 # Copy the Go Modules manifests
-COPY go.mod go.mod
-COPY go.sum go.sum
+COPY go.mod 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 the go source
-COPY main.go main.go
-COPY api/ api/
-COPY controllers/ controllers/
-COPY github/ github/
+COPY . .
 
 # Build
-RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 GO111MODULE=on go build -a -o manager main.go
+RUN export GOOS=$(echo ${TARGETPLATFORM} | cut -d / -f1) && \
+  export GOARCH=$(echo ${TARGETPLATFORM} | cut -d / -f2) && \
+  GOARM=$(echo ${TARGETPLATFORM} | cut -d / -f3 | cut -c2-) && \
+  go build -a -o manager main.go
 
 # Use distroless as minimal base image to package the manager binary
 # Refer to https://github.com/GoogleContainerTools/distroless for more details
 FROM gcr.io/distroless/static:nonroot
+
 WORKDIR /
+
 COPY --from=builder /workspace/manager .
+
 USER nonroot:nonroot
 
 ENTRYPOINT ["/manager"]