add configuration to use django sample with Docker Dev Environments feature (#252)

Signed-off-by: Guillaume Lours <guillaume.lours@docker.com>

django/app/Dockerfile

@@ -1,4 +1,6 @@
-FROM python:3.7-alpine 
+# syntax=docker/dockerfile:1.4
+
+FROM --platform=$BUILDPLATFORM python:3.7-alpine AS builder
 EXPOSE 8000
 WORKDIR /app 
 COPY requirements.txt /app
@@ -6,3 +8,17 @@ RUN pip3 install -r requirements.txt --no-cache-dir
 COPY . /app 
 ENTRYPOINT ["python3"] 
 CMD ["manage.py", "runserver", "0.0.0.0:8000"]
+
+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 ["manage.py", "runserver", "0.0.0.0:8000"]