Update dev container configuration for monorepo

.devcontainer/backend/docker-compose.yml

@@ -0,0 +1,19 @@
+services:
+  app:
+    image: mcr.microsoft.com/devcontainers/python:3.12-bookworm
+    volumes:
+      - ../..:/simple-ocpp-cs:cached
+    command: sleep infinity
+
+  db:
+    image: postgres:17
+    restart: unless-stopped
+    volumes:
+      - postgres-data:/var/lib/postgresql/data
+    environment:
+      POSTGRES_USER: postgres
+      POSTGRES_DB: postgres
+      POSTGRES_PASSWORD: postgres
+
+volumes:
+  postgres-data: