flask-redis: dev envs support & misc improvements (#265)

(Most of this is almost identical to #263.)

* Docker Desktop Development Environments config
* Use cache volumes for pip
* Downgrade from Python 3.11 _alpha_ -> Python 3.10
* Use port `8000` to avoid conflicts with Airplay on
    macOS for default Flask port `5000`
* Use `SIGINT` to gracefully stop Flask
* Formatting fixes in `compose.yaml`

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

flask-redis/Dockerfile

@@ -1,6 +1,27 @@
-FROM python:3.11.0a6-alpine3.15
+# syntax=docker/dockerfile:1.4
+FROM --platform=$BUILDPLATFORM python:3.10-alpine AS builder
+
 WORKDIR /code
+
 COPY requirements.txt /code
-RUN pip install -r requirements.txt --no-cache-dir
+RUN --mount=type=cache,target=/root/.cache/pip \
+    pip3 install -r requirements.txt
+
 COPY . /code
-CMD python app.py
+
+ENTRYPOINT ["python3"]
+CMD ["app.py"]
+
+FROM builder as dev-envs
+
+RUN <<EOF
+apk update
+apk add git bash
+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 / /