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/compose.yaml

@@ -1,13 +1,18 @@
 services:
-   redis: 
-     image: redislabs/redismod
-     ports:
-       - '6379:6379' 
-   web:
-        build: .
-        ports:
-            - "5000:5000"
-        volumes:
-            - .:/code
-        depends_on:
-            - redis
+  redis:
+    image: redislabs/redismod
+    ports:
+      - '6379:6379'
+  web:
+    build:
+      context: .
+      target: builder
+    # flask requires SIGINT to stop gracefully
+    # (default stop signal from Compose is SIGTERM)
+    stop_signal: SIGINT
+    ports:
+      - '8000:8000'
+    volumes:
+      - .:/code
+    depends_on:
+      - redis