remove multistep build, build go last, allowing cached build layers (#1903)

Dockerfile.debug

@@ -2,31 +2,24 @@
 # and are in no way endorsed by Headscale's maintainers as an
 # official nor supported release or distribution.
 
-FROM docker.io/golang:1.22-bookworm AS build
+FROM docker.io/golang:1.22-bookworm
 ARG VERSION=dev
 ENV GOPATH /go
 WORKDIR /go/src/headscale
 
-COPY go.mod go.sum /go/src/headscale/
-RUN go mod download
-
-COPY . .
-
-RUN CGO_ENABLED=0 GOOS=linux go install -ldflags="-s -w -X github.com/juanfont/headscale/cmd/headscale/cli.Version=$VERSION" -a ./cmd/headscale
-RUN test -e /go/bin/headscale
-
-# Debug image
-FROM docker.io/golang:1.22-bookworm
-
-COPY --from=build /go/bin/headscale /bin/headscale
-ENV TZ UTC
-
 RUN apt-get update \
   && apt-get install --no-install-recommends --yes less jq \
   && rm -rf /var/lib/apt/lists/* \
   && apt-get clean
 RUN mkdir -p /var/run/headscale
 
+COPY go.mod go.sum /go/src/headscale/
+RUN go mod download
+
+COPY . .
+
+RUN CGO_ENABLED=0 GOOS=linux go install -ldflags="-s -w -X github.com/juanfont/headscale/cmd/headscale/cli.Version=$VERSION" -a ./cmd/headscale && test -e /go/bin/headscale
+
 # Need to reset the entrypoint or everything will run as a busybox script
 ENTRYPOINT []
 EXPOSE 8080/tcp