Add docker-compose file for PostgreSQL service

Introduces a docker-compose.yaml file to set up a PostgreSQL container named "neptune-db". Configures the container with environment variables and volumes for persistent data storage.

docker-compose.yaml

@@ -0,0 +1,14 @@
+services:
+  database:
+    container_name: "neptune-db"
+    image: 'postgres:latest'
+    env_file:
+      - .env
+    ports:
+      - "${POSTGRES_PORT}:5432"
+    environment:
+      POSTGRES_USER: ${POSTGRES_USER}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
+      POSTGRES_DB: ${POSTGRES_DATABASE}
+    volumes:
+      - './db-data/:/var/lib/postgresql/data/'