add configuration to use react-rust-postgres sample with Docker Dev Environments feature (#264)

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

react-rust-postgres/backend/Dockerfile

@@ -1,3 +1,4 @@
+# syntax=docker/dockerfile:1.4
 FROM rust:buster AS base
 
 ENV USER=root
@@ -16,6 +17,23 @@ EXPOSE 8000
 
 CMD [ "cargo", "run", "--offline" ]
 
+FROM base AS dev-envs
+
+EXPOSE 8000
+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 [ "cargo", "run", "--offline" ]
+
 FROM base AS builder
 
 RUN cargo build --release --offline