Dockerfile.multi-stage: Use toolchain from inside container

This allows for easy cross-compilation

Author: siretart

Dockerfile.multi-stage

@@ -0,0 +1,21 @@
+FROM golang:1.20 as build
+
+WORKDIR /app
+
+# pre-copy/cache go.mod for pre-downloading dependencies and only redownloading them in subsequent builds if they change
+COPY go.mod go.sum ./
+RUN go mod download && go mod verify
+
+COPY . .
+RUN go build -v  ./...
+
+
+FROM debian:testing-slim
+
+EXPOSE 9436
+
+COPY scripts/start.sh /app/
+COPY --from=build /app/mikrotik-exporter /app/mikrotik-exporter
+RUN chmod 755 /app/*
+
+ENTRYPOINT ["/app/start.sh"]