ci: fix few Docker issues and use multi stage builds for a lighter image

Dockerfile

@@ -1,4 +1,6 @@
-FROM golang:1.19.4-alpine3.17
+FROM golang:1.22.1-alpine3.19 as build
+
+RUN apk add make git
 
 WORKDIR /code
 
@@ -8,6 +10,17 @@ RUN go mod download
 COPY . .
 RUN make build
 
+FROM alpine:3.19
+
+RUN adduser user -D
+
+USER user
+WORKDIR /home/user/dumb
+
+COPY --from=build /code/dumb .
+COPY --from=build /code/static static
+
 EXPOSE 5555/tcp
 
-CMD ["/code/dumb"]
+CMD ["./dumb"]
+