consolidated all 0.81 rcs entries in the changelog into 0.81 (#53212)

Summary:
Changelog: [Internal]

Pull Request resolved: #53212

Reviewed By: cortinico

Differential Revision: D80005041

Pulled By: vzaidman

fbshipit-source-id: 93f570d9ddccdf8d4febc9d9f7702646ad7a6b56

Author: vzaidman