Apply custom headers in RCTBundleURLProvider (#55608)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/55608

Inject custom devsupport headers into the packager status check request. Changes NSURLRequest to NSMutableURLRequest to allow header mutation before the request is sent.

Changelog:
[Internal] [Changed] -

Reviewed By: cipolleschi

Differential Revision: D93596717

fbshipit-source-id: 94ab3df95317cb3697d26d18b6a27750bfcf4bff