add 0.81.0-rc.0 release to the changelog file (#52517)

Summary:
Changelog: [INTERNAL] - Update the changelog to include `0.81.0-rc.0`

Pull Request resolved: #52517

Reviewed By: cortinico

Differential Revision: D78021431

Pulled By: vzaidman

fbshipit-source-id: 3053aed68a947bf808ae29d4827599112175f531

Author: vzaidman