Move all the infrastructure to test nightlies out of facebook/react-native (#53280)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/53280

I've moved a lot of the nightly testing infrastructure on a RNC repo here:
https://github.com/react-native-community/nightly-tests/

This allows us to iterate faster without having to wait for diffs to be
imported and test inside fbsource.

Changelog:
[Internal] [Changed] -

Reviewed By: cipolleschi

Differential Revision: D80262856

fbshipit-source-id: dc2dfe75901ac78ec9f6e940540102276d34acdf