wpcom Features: add new Holiday Snow feature (#40478)

This commit brings a new feature to the mu-wpcom package:

- That feature can be toggled via Settings > General in wp-admin.
- It is active from December 1st to January 4th by default.

Committed via a GitHub action: https://github.com/Automattic/jetpack/actions/runs/12201507312

Upstream-Ref: Automattic/jetpack@d416736

composer.json

@@ -10,7 +10,7 @@
 		"automattic/jetpack-connection": "^6.2.0-alpha",
 		"automattic/jetpack-logo": "^3.0.0",
 		"automattic/jetpack-status": "^5.0.1",
-		"automattic/jetpack-sync": "^4.0.2"
+		"automattic/jetpack-sync": "^4.1.0-alpha"
 	},
 	"require-dev": {
 		"yoast/phpunit-polyfills": "^1.1.1",