docs: fix url for chainreactconf (#30199)

Summary:
Fixed URL of ChainReactConf website on the ECOSYSTEM.md

## Changelog

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[Internal] [Fixed] - Fix URL of ChainReactConf Website

Pull Request resolved: https://github.com/facebook/react-native/pull/30199

Test Plan: URL leads to the ChainReactConf website

Reviewed By: makovkastar

Differential Revision: D24386708

Pulled By: cpojer

fbshipit-source-id: 27a48e84547ef3bc067845b3c302dd57decc34b2