Make base API path configurable via env variable

backend/src/app.ts

@@ -4,14 +4,14 @@ import morgan from 'morgan';
 import router from './router';
 import wxService from './services/wx.service';
 
-const { PORT = 3000 } = process.env;
+const { PORT = 3000, BASE_PATH = '/api' } = process.env;
 
 const app = express();
 
 app.set('trust proxy', true);
 app.use(morgan('combined'));
 
-app.use('/api', router.router);
+app.use(BASE_PATH, router.router);
 
 const frontendRoot = '/opt/frontend/dist';
 app.use(express.static(frontendRoot));