As far as I know, the best way would be for fidel-react-native to do whatever’s needed to have Autolinking take care of it for you. I might be wrong, but I think Autolinking normally handles that sort of thing for you.
If you do actually need to add it yourself, then yes, you’d need a Config Plugin. Try searching in the expo/expo, expo/expo-cli, expo/config-plugins repositories (and maybe elsewhere on GitHub) for usages of withProjectBuildGradle.