Explictly set 'Content-Type': 'application/json'

[ptpaterson]

Requests will fail in some environments if we do not set content type explicitly.

See this Stack Overflow question where the resolution was to add provide 'Content-Type': 'application/json' header to the client configuration.

https://stackoverflow.com/questions/75437045/react-native-connect-faunadb-typeerror-network-request-failed-on-android

[github-actions[bot]]

Internal ticket number is FE-3077