add changelog for 0.70 (#34202)

Summary:
# WIP

Adds changelog for new release.

## Changelog

<!-- Help reviewers and the release process by writing your own changelog entry. For an example, see:
https://reactnative.dev/contributing/changelogs-in-pull-requests
-->

[Internal] [Changed] - add changelog entry for 0.70.0

Pull Request resolved: #34202

Test Plan: N/A

Reviewed By: cortinico, cipolleschi

Differential Revision: D39258933

Pulled By: dmytrorykun

fbshipit-source-id: 3aa19301b47aa8cacd5afe35015c2820e96ab4fa