Enable SonarKit and Flipper in React-Core (facebook#33499)

Summary:
Pull Request resolved: facebook#33499

This DIFF turns on the `FB_SONARKIT_ENABLED` flag when installing Flipper ina RN app. The flag is enabled only in Debug config, given that Flipper is installed only in this configuration.

This PR also fixes this issue: facebook#33497

This PR is required because release 0.67 has the Flag in the app, while release 0.68 moved it in the React-Core pod.
We can't enable the flag at the `React-Core.podspec` level because we should not make assumptions on whether users want flipper or not.

## Changelog
[iOS][Changed] - Enable SonarKit in React-Core when the configuration is `'Debug'`

Reviewed By: cortinico

Differential Revision: D35141506

fbshipit-source-id: 171b7fa8ea7727c633ef963408e86b332c32e9fa

scripts/react_native_pods.rb

@@ -194,6 +194,15 @@ def flipper_post_install(installer)
         config.build_settings['SWIFT_VERSION'] = '4.1'
       end
     end
+
+    # Enable flipper for React-Core Debug configuration
+    if target.name == 'React-Core'
+      target.build_configurations.each do |config|
+        if config.name == 'Debug'
+          config.build_settings['OTHER_CFLAGS'] = "$(inherited) -DFB_SONARKIT_ENABLED=1"
+        end
+      end
+    end
   end
 end