feat(docker): Improve Dockerfile

- include build process in Dockerfile
- use multistage build process

Dockerfile

@@ -1,3 +1,26 @@
-FROM scratch
+# syntax=docker/dockerfile:1
+# Based on https://docs.docker.com/language/golang/build-images/#multi-stage-builds
+
+# Build the application from source
+FROM golang:1.22
+
+WORKDIR /app
+
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY *.go ./
+
+ARG CGO_ENABLED=0
+ARG GOARCH=amd64
+ARG GOOS=linux
+RUN go build -ldflags '-s -w' -trimpath -o /docker-etchosts
+
+# Deploy the application binary into a lean image
+FROM scratch AS build-release-stage
+
+WORKDIR /
+
+COPY --from=0 /docker-etchosts /docker-etchosts
+
 ENTRYPOINT ["/docker-etchosts"]
-COPY docker-etchosts /