fix: configurable changelog url (#2418)

apps/web/preset.config.mjs

@@ -33,4 +33,7 @@ export const buildFlags = {
   enableDebugPage: Boolean(
     process.env.ENABLE_DEBUG_PAGE ?? process.env.NODE_ENV === 'development'
   ),
+  changelogUrl:
+    process.env.CHANGELOG_URL ??
+    'https://affine.pro/blog/whats-new-affine-0518',
 };