meta(changelog): Update changelog for 10.0.0-beta.0 (#17222)

Author: andreiborza

CHANGELOG.md

@@ -6,6 +6,15 @@
 
 Work in this release was contributed by @richardjelinek-fastest. Thank you for your contribution!
 
+## 10.0.0-beta.0
+
+This is a beta release of the upcoming major release of version 10.
+This release does not yet entail a comprehensive changelog as version 10 is not yet stable.
+
+For this release's iteration of the migration guide, see the [Migration Guide as per `10.0.0-beta.0`](https://github.com/getsentry/sentry-javascript/blob/d059b06254251507792369171a7f7a3d5a1d7640/MIGRATION.md?plain=1#L11).
+
+Please note that the migration guide is work in progress and subject to change.
+
 ## 9.40.0
 
 ### Important Changes