nginx-flask-mysql: add dev envs support (#272)

* Add Docker Desktop Development Environments config
* Change port `5000` -> `8000` for Flask to avoid conflicts on
  recent macOS versions
* Improve DB health check (for non-dev envs case) to avoid
  producing a bunch of log spam

Co-authored-by: Guillaume Lours <guillaume@lours.me>
Signed-off-by: Milas Bowman <milas.bowman@docker.com>

nginx-flask-mysql/.docker/docker-compose.yaml

@@ -0,0 +1,61 @@
+services:
+  db:
+    image: mariadb:10-focal
+    command: '--default-authentication-plugin=mysql_native_password'
+    restart: always
+    healthcheck:
+      test: ["CMD", "mysqladmin", "ping", "-h", "127.0.0.1", "--silent"]
+      interval: 3s
+      retries: 5
+      start_period: 30s
+    secrets:
+      - db-password
+    volumes:
+      - db-data:/var/lib/mysql
+    networks:
+      - backnet
+    environment:
+      - MYSQL_DATABASE=example
+      - MYSQL_ROOT_PASSWORD_FILE=/run/secrets/db-password
+    expose:
+      - 3306
+      - 33060
+
+  backend:
+    build:
+      context: backend
+      target: dev-envs
+    restart: always
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+    secrets:
+      - db-password
+    ports:
+      - 8000:8000
+    networks:
+      - backnet
+      - frontnet
+    depends_on:
+      db:
+        condition: service_healthy
+
+  proxy:
+    build: proxy
+    restart: always
+    ports:
+      - 80:80
+    depends_on: 
+      - backend
+    networks:
+      - frontnet
+
+volumes:
+  db-data:
+
+secrets:
+  db-password:
+    file: db/password.txt
+
+networks:
+  backnet:
+  frontnet: