add configuration to use react-express-mongo sample with Docker Dev Environments feature (#271)

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

react-express-mongodb/backend/Dockerfile

@@ -1,4 +1,6 @@
-FROM node:lts-buster-slim
+# syntax=docker/dockerfile:1.4
+
+FROM node:lts-buster-slim AS development
 
 # Create app directory
 WORKDIR /usr/src/app
@@ -12,3 +14,18 @@ COPY . /usr/src/app
 EXPOSE 3000
 
 CMD [ "npm", "run", "dev" ]
+
+FROM development as dev-envs
+RUN <<EOF
+apt-get update
+apt-get install -y --no-install-recommends git
+EOF
+
+RUN <<EOF
+useradd -s /bin/bash -m vscode
+groupadd docker
+usermod -aG docker vscode
+EOF
+# install Docker tools (cli, buildx, compose)
+COPY --from=gloursdocker/docker / /
+CMD [ "npm", "run", "dev" ]