Add example environment configuration file

Author: yihong1120

.env.example

@@ -0,0 +1,22 @@
+# Database
+DATABASE_URL='mysql+aiomysql://username:password@mysql/construction_hazard_detection'
+
+# API Credentials
+API_USERNAME='user'
+API_PASSWORD='password'
+
+# API URLs
+DETECT_API_URL = "http://127.0.0.1:8000"
+FCM_API_URL = "http://127.0.0.1:8003"
+VIOLATION_RECORD_API_URL = "http://127.0.0.1:8002"
+STREAMING_API_URL = "http://127.0.0.1:8800"
+DB_MANAGEMENT_API_URL = "http://127.0.0.1:8005"
+
+# Redis
+REDIS_HOST = '127.0.0.1'
+REDIS_PORT = 6379
+REDIS_PASSWORD = 'password'
+
+# Firebase
+FIREBASE_CRED_PATH = 'examples/local_notification_server/your-firebase-adminsdk.json'
+project_id = 'your-project-id'