nginx-aspnet-mysql: add dev envs configuration (#267)

* nginx-aspnet-mysql: add dev envs configuration
* Fix/enable MySQL/MariaDB health check
* Refactor `Dockerfile` for use as Compose app as well as with
  dev envs
* nginx-aspnet-mysql: remove DB healthcheck from dev envs config

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

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

@@ -0,0 +1,38 @@
+services:
+  backend:
+    build:
+      context: backend
+      target: dev-envs
+    restart: always
+    secrets:
+      - db-password
+    depends_on: ['db']
+    environment:
+      - ASPNETCORE_URLS=http://+:8000
+    volumes:
+      - /var/run/docker.sock:/var/run/docker.sock
+
+  db:
+    image: mariadb:10-focal
+    command: '--default-authentication-plugin=mysql_native_password'
+    restart: always
+    secrets:
+      - db-password
+    volumes:
+      - db-data:/var/lib/mysql
+    environment:
+      - MYSQL_DATABASE=example
+      - MYSQL_ROOT_PASSWORD_FILE=/run/secrets/db-password
+
+  proxy:
+    build: proxy
+    ports:
+      - 80:80
+    depends_on: 
+      - backend
+
+volumes:
+  db-data:
+secrets:
+  db-password:
+    file: db/password.txt