Add updated Dockerfile

Dockerfile

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+# Build the manager binary
+FROM golang:1.15.2 as builder
+
+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 the go source
+COPY main.go main.go
+COPY internal/ internal/
+COPY pkg/ pkg/
+
+# Build
+RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 GO111MODULE=on go build  -mod=mod -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
+
+# Port for metrics and probes
+EXPOSE 9090
+
+ENTRYPOINT ["/manager"]