build: 🏗️ use Docker multi-stage build

Dockerfile

@@ -1,4 +1,4 @@
-FROM golang:1.21
+FROM golang:1.21 as build
 
 # Set destination for COPY
 WORKDIR /app
@@ -14,6 +14,10 @@ COPY . ./
 # Build
 RUN CGO_ENABLED=0 GOOS=linux go build -o /listy
 
+FROM alpine
+
+COPY --from=build /listy /listy
+
 # Optional:
 # To bind to a TCP port, runtime parameters must be supplied to the docker command.
 # But we can document in the Dockerfile what ports