feat: use TARGETARCH to support cross-platform multi-arch builds (#97)

On-behalf-of: @SAP <simon@simontesar.com>

Author: simontesar

Dockerfile

@@ -1,25 +1,19 @@
 FROM --platform=$BUILDPLATFORM golang:1.25@sha256:36b4f45d2874905b9e8573b783292629bcb346d0a70d8d7150b6df545234818f AS builder
+ARG TARGETARCH
 
 WORKDIR /workspace
 
 COPY go.mod go.sum ./
-RUN --mount=type=cache,target=/go/pkg/mod \
-    go mod download && go mod verify
+RUN go mod download
 
 COPY . .
-RUN --mount=type=cache,target=/go/pkg/mod/ \
-    --mount=type=cache,target=/root/.cache/go-build \
-    CGO_ENABLED=0 \
-    GOCACHE=/root/.cache/go-build \
-    GOOS=$TARGETOS \
-    GOARCH=$TARGETARCH \
-    make build
+RUN CGO_ENABLED=0 GOOS=linux GOARCH=${TARGETARCH} go build -a -o manager cmd/main.go
 
 # Use distroless base-debian11 image to include shell access while keeping minimal footprint
 # Refer to https://github.com/GoogleContainerTools/distroless for more details
 FROM gcr.io/distroless/base-debian11:debug@sha256:68e5ea65df0f5d135083d4cc1df5fc16855d61ed628254df8e1affa8ce2d3244
 WORKDIR /
-COPY --from=builder /workspace/bin/manager .
+COPY --from=builder /workspace/manager .
 USER 65532:65532
 
 ENTRYPOINT ["/manager"]