optimize dockerfile

cmd/Dockerfile

@@ -1,6 +1,4 @@
-FROM golang:1.18-alpine AS build
-
-ARG VERSION=dev
+FROM --platform=$BUILDPLATFORM golang:1.18-alpine AS build
 
 WORKDIR /build
 
@@ -10,7 +8,16 @@ RUN go mod download
 
 COPY . .
 
-RUN CGO_ENABLED=0 go build -ldflags="-X 'main.version=${VERSION}'-w -s" -o bot cmd/main.go
+ARG TARGETOS
+ARG TARGETARCH
+ARG VERSION=dev
+
+RUN --mount=type=cache,target=/root/.cache/go-build \
+    --mount=type=cache,target=/go/pkg \
+    CGO_ENABLED=0 \
+    GOOS=$TARGETOS \
+    GOARCH=$TARGETARCH \
+    go build -ldflags="-X 'main.version=${VERSION}'-w -s" -o bot cmd/main.go
 
 FROM alpine