Update draft release notes for 21.4.

Author: wpmobilebot

WooCommerce/Resources/release_notes.txt

@@ -1,3 +1,4 @@
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-This update brings enhanced reliability and clarity to your WooCommerce experience! Enjoy improved Jetpack setup, smoother media handling, and better product and payment workflows. We’ve also optimized storage and addressed key UI issues to elevate performance. Plus, Tap to Pay onboarding now guides you with ease!
+- [**] Store Picker: Sites can now be hidden from the list for a more focused experience for agencies. [https://github.com/woocommerce/woocommerce-ios/pull/14780]
+- [*] Fetching plugins info in the app (e.g. payments onboarding) is more resilient to unexpected types in unrelated fields in the system status response. This used to result in a decoding error. [https://github.com/woocommerce/woocommerce-ios/pull/14781]
+- [*] Fixed an issue on iPad where creating an order with a custom amount type failed after selecting and deselecting a product. [https://github.com/woocommerce/woocommerce-ios/pull/14789]