Polish the changelog for 0.80

Summary:
I've done a pass and cleaned up the changelog for 0.80 ahead of the release

Changelog:
[Internal] -

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Reviewed By: fabriziocucci, cipolleschi

Differential Revision: D76511997

fbshipit-source-id: 3872f9adbf16767c466e4dbb72d70fdaf2defde3

Author: cortinico