split the changelog into decades (#38017)

Summary:
Well, looks like we've hit a GH limit 🤣

<img width="1272" alt="Screenshot 2023-06-22 at 10 32 19" src="https://github.com/facebook/react-native/assets/16104054/d1901d7c-a06b-4dae-9ec4-1846dc458eb1">

This PR splits the changelog into (for lack of better term) decades:

* lower than 0.60 (turns out we only started having proper changelogs in the mid 0.50-ish)
* 60->69
* 70+

This also works well because anything lower than 0.70 is now in the unsupported range.

## Changelog:

<!-- Help reviewers and the release process by writing your own changelog entry.

Pick one each for the category and type tags:

[ANDROID|GENERAL|IOS|INTERNAL] [BREAKING|ADDED|CHANGED|DEPRECATED|REMOVED|FIXED|SECURITY] - Message

For more details, see:
https://reactnative.dev/contributing/changelogs-in-pull-requests
-->

[Internal] [Changed] - split the changelog into decades

Pull Request resolved: #38017

Test Plan: N/A

Reviewed By: GijsWeterings

Differential Revision: D46932308

Pulled By: cipolleschi

fbshipit-source-id: f384d24cdf73c932b0b560919ac732bd993e93da

Author: kelset