feat: add optional debug logging

Adds an optional debug logging feature that can be enabled by setting the DEBUG environment variable.

This allows developers to more easily debug issues related to the Notion API client.

src/lib/notionClient.js

@@ -4,7 +4,9 @@ import dotenv from 'dotenv';
 
 // Load environment variables from .env file
 dotenv.config();
-console.log('Environment variables:', process.env);
+if (process.env.DEBUG) {
+  console.log('Environment variables:', process.env);
+}
 
 if (!process.env.NOTION_API_KEY) {
   throw new Error("NOTION_API_KEY is not defined in the environment variables.");