Sync CHANGELOG.md

[rogercoll]

The CHANGELOG.md file is outdated.

• Is there any reason why we are not updating it?

On the notes for each release we write the changes but in case of an hypothetical VCS migration, those notes would be lost and hard to re-create. If we publish the release notes in NewRelic public documentation, we could put the link on the CHANGELOG.md file instead of syncing the file since the last added version.