Refactor Dockerfile to build Go binary outside of Docker (#218)

This change moves building the Go binary out of the Dockerfile, and also
fixes some issues in the makefile. These things will speed up build
times and avoid rebuilding when not needed. Additionally it will make
getting version data easier to use as part of the user agent.

Signed-off-by: Philip Laine <philip.laine@gmail.com>

Dockerfile

@@ -1,36 +1,11 @@
-# This dockerfile is used for tests and local builds
-
-# Build the manager binary
-FROM docker.io/golang:1.26 AS builder
+FROM gcr.io/distroless/static:nonroot
 ARG TARGETOS
 ARG TARGETARCH
-
-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 cmd/main.go cmd/main.go
-COPY api/ api/
-COPY internal/ internal/
-COPY pkg/ pkg/
-
-# Build
-# the GOARCH has not a default value to allow the binary be built according to the host where the command
-# was called. For example, if we call make docker-build in a local env which has the Apple Silicon M1 SO
-# the docker BUILDPLATFORM arg will be linux/arm64 when for Apple x86 it will be linux/amd64. Therefore,
-# by leaving it empty we can ensure that the container and binary shipped on it will have the same platform.
-RUN CGO_ENABLED=0 GOOS=${TARGETOS:-linux} GOARCH=${TARGETARCH} go build -ldflags="-w -s" -a -o manager cmd/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 .
+LABEL org.opencontainers.image.title="NetBird Operator" \
+      org.opencontainers.image.description="Kubernetes operator for NetBird." \
+      org.opencontainers.image.source="https://github.com/netbirdio/kubernetes-operator" \
+      org.opencontainers.image.vendor="NetBird" \
+      org.opencontainers.image.licenses="BSD-3-Clause"
+COPY bin/${TARGETOS}-${TARGETARCH}/netbird-operator .
 USER 65532:65532
-
-ENTRYPOINT ["/manager"]
+ENTRYPOINT ["/netbird-operator"]