chore(stalebot): set the stale bot to start from oldest (#36337)

Summary:
We realized lately that the bot has "too much to eat" and because by default it starts from the most recent things ([see default here](https://github.com/actions/stale#ascending)), I'm fixing the settings so that it would start from oldest.

This should make it start from [very old and inactive issues](https://github.com/facebook/react-native/issues?q=is%3Aissue+is%3Aopen+sort%3Aupdated-asc+) such as such as https://github.com/facebook/react-native/issues/1693 (last comment from Aug 2020) or https://github.com/facebook/react-native/issues/10027 (last activity in May 2019) and make it do significant progress on the repo clean up :)

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[INTERNAL] [CHANGED] - set the stale bot to start from oldest

Pull Request resolved: https://github.com/facebook/react-native/pull/36337

Test Plan: N/A

Reviewed By: cortinico

Differential Revision: D43694724

Pulled By: cipolleschi

fbshipit-source-id: a7cc07e4669b1d7f5e0bfc31ff313767790e1f0f