WIP release notes

Author: SkiFire13

release-content/release-notes/dynamic-bundles.md

@@ -0,0 +1,15 @@
+---
+title: Option and dynamic bundles
+authors: ["@SkiFire13"]
+pull_requests: [19491]
+---
+
+Until now bundles have always represented a static set of components, meaning you could not create a `Bundle` that sometimes inserts a component and sometimes doesn't, or a totally dynamic bundle like you would expect from a `Box<dyn Bundle>`.
+
+In Bevy 0.17 the `Bundle` trait has been reworked to support these usecases, in particular:
+
+- `Option<B: Bundle` now implements `Bundle`
+- `Bundle` is now a dyn-compatible trait and `Box<dyn Bundle>` implements `Bundle`
+- `Vec<Box<dyn Bundle>>` also implements `Bundle`
+
+TODO: showcase