Add Dockerfile.

Dockerfile

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+# Use buildx for multi-architecture support
+FROM --platform=${BUILDPLATFORM} golang:1.21 AS builder
+
+WORKDIR /app
+
+# Copy go.mod and go.sum files to download dependencies
+COPY go.mod go.sum ./
+RUN go mod download
+
+# Copy the source code into the container
+COPY . .
+
+# Build the application for the specified target architecture
+RUN CGO_ENABLED=0 GOOS=linux GOARCH=${TARGETARCH} go build -o mqtt-postgresql .
+
+# Create a minimal runtime image
+FROM --platform=${TARGETPLATFORM} scratch
+
+WORKDIR /app
+
+# Copy the executable from the builder stage
+COPY --from=builder /app/mqtt-postgresql /app/mqtt-postgresql
+COPY --from=builder /etc/ssl/certs/ca-certificates.crt /etc/ssl/certs/
+
+# Run the application
+CMD ["./mqtt-postgresql"]