add multiplatform img support

backend/dockerfile

@@ -1,14 +1,17 @@
-FROM arm64v8/golang:1.22.2-alpine as build
+FROM --platform=$BUILDPLATFORM golang:alpine AS build
+
+ARG TARGETOS
+ARG TARGETARCH
 
 WORKDIR /app
 
 COPY . .
 
-RUN GOOS=linux GOARCH=arm64 go build -o backend
+RUN GOOS=${TARGETOS} GOARCH=${TARGETARCH} go build -o backend
 
 RUN apk update && apk add ca-certificates && update-ca-certificates
 
-FROM arm64v8/busybox:1.36.1
+FROM --platform=$TARGETPLATFORM busybox:1.36.1
 
 COPY --from=build /etc/ssl/certs /etc/ssl/certs
 COPY --from=build /app/backend /app/