nginx-golang: add dev envs support (#273)

* Add Docker Desktop Developer Environments config
* Upgrade from Go 1.13 (🙀) to 1.18
* Rename `frontend` -> `proxy` for clarity & consistency
  with other samples
* Add Chi as a dependency to provide an example of Go
  module dependencies for parity with other samples

Signed-off-by: Milas Bowman <milas.bowman@docker.com>

nginx-golang/backend/Dockerfile

@@ -1,11 +1,41 @@
-FROM golang:1.13 AS build
+# syntax=docker/dockerfile:1.4
+FROM --platform=$BUILDPLATFORM golang:1.18-alpine AS builder
 
-WORKDIR /compose/hello-docker
-COPY main.go main.go
-RUN CGO_ENABLED=0 go build -o backend main.go
+WORKDIR /code
+
+ENV CGO_ENABLED 0
+ENV GOPATH /go
+ENV GOCACHE /go-build
+
+COPY go.mod go.sum ./
+RUN --mount=type=cache,target=/go/pkg/mod/cache \
+    go mod download
+
+COPY . .
+
+RUN --mount=type=cache,target=/go/pkg/mod/cache \
+    --mount=type=cache,target=/go-build \
+    go build -o bin/backend main.go
+
+CMD ["/code/bin/backend"]
+
+FROM builder as dev-envs
+
+RUN <<EOF
+apk update
+apk add git
+EOF
+
+RUN <<EOF
+addgroup -S docker
+adduser -S --shell /bin/bash --ingroup docker vscode
+EOF
+
+# install Docker tools (cli, buildx, compose)
+COPY --from=gloursdocker/docker / /
+
+CMD ["go", "run", "main.go"]
 
 FROM scratch
-COPY --from=build /compose/hello-docker/backend /usr/local/bin/backend
+COPY --from=builder /code/bin/backend /usr/local/bin/backend
 CMD ["/usr/local/bin/backend"]
-
-