docker: add wait-for-mqtt entrypoint; remove compose override

Dockerfile

@@ -11,7 +11,9 @@ RUN CGO_ENABLED=0 GOOS=linux GOARCH=amd64 \
 
 # Final image
 FROM alpine:3.18
-RUN apk add --no-cache ca-certificates
+RUN apk add --no-cache ca-certificates netcat-openbsd
 COPY --from=builder /app/server /usr/local/bin/server
+COPY scripts/wait-for-mqtt.sh /usr/local/bin/wait-for-mqtt.sh
+RUN chmod +x /usr/local/bin/wait-for-mqtt.sh
 EXPOSE 8080
-ENTRYPOINT ["/usr/local/bin/server"]
+ENTRYPOINT ["/usr/local/bin/wait-for-mqtt.sh"]