Add .env-example file and update configuration for environment variables

- Created .env-example for environment variable setup
- Updated README to reflect changes in .env file creation
- Modified config.py to include new environment variables and DATABASE_URL property
- Enhanced database.py with connect and disconnect functions
- Updated main.py to manage database connection lifecycle
- Adjusted compose.yaml for consistent environment variable usage

compose.yaml

@@ -1,14 +1,12 @@
 services:
   api:
     restart: unless-stopped
-    container_name: api_${postgres_db}
+    container_name: api_${POSTGRES_DB}
     build: .
     env_file:
       - .env
     ports:
-      - "${api_port}:8000"
-    environment:
-      DATABASE_URL: postgresql+asyncpg://${postgres_user}:${postgres_password}@db:${db_port}/${postgres_db}
+      - "${API_PORT}:8000"
     depends_on:
       db:
         condition: service_healthy
@@ -17,20 +15,20 @@ services:
 
   db:
     image: postgres:18-alpine
-    container_name: postgres_${postgres_db}
+    container_name: postgres_${POSTGRES_DB}
     restart: unless-stopped
     shm_size: 128mb
-    ports:
-      - ${db_port}:5432
+    #ports:   #Not needed as the API container will connect to the DB container using the internal Docker network. Uncomment if you want to access the database from outside the Docker network.
+    #  - 5432:5432
     volumes:
       - ./postgresData:/var/lib/postgresql/data
       - ./Create.sql:/docker-entrypoint-initdb.d/Create.sql
     environment:
-      POSTGRES_USER: ${postgres_user}
-      POSTGRES_PASSWORD: ${postgres_password}
-      POSTGRES_DB: ${postgres_db}
+      POSTGRES_USER: ${POSTGRES_USER}
+      POSTGRES_PASSWORD: ${POSTGRES_PASSWORD}
+      POSTGRES_DB: ${POSTGRES_DB}
     healthcheck:
-      test: ["CMD-SHELL", "pg_isready -U ${postgres_user} -d ${postgres_db}"]
+      test: ["CMD-SHELL", "pg_isready -U ${POSTGRES_USER} -d ${POSTGRES_DB}"]
       interval: 10s
       timeout: 5s
       retries: 5