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/app.py

@@ -11,4 +11,4 @@ def hello():
     return "This webpage has been viewed "+counter+" time(s)"
 
 if __name__ == "__main__":
-    app.run(host="0.0.0.0", debug=True)
+    app.run(host="0.0.0.0", port=8000, debug=True)