Added dockerfile

Signed-off-by: Marcus Noble <github@marcusnoble.co.uk>

Dockerfile

@@ -0,0 +1,11 @@
+FROM golang:1.25-alpine AS builder
+WORKDIR /app/
+ADD go.mod go.sum ./
+RUN go mod download
+ADD . .
+RUN GOOS=linux GOARCH=amd64 CGO_ENABLED=0 go build -ldflags="-w -s" -o online-exporter main.go
+
+FROM golang:1.25-alpine
+WORKDIR /app/
+COPY --from=builder /app/online-exporter /app/online-exporter
+ENTRYPOINT ["/app/online-exporter"]