Move expo samples to a service account.

Summary:
This is a nit. Just moving this expo sample to a service account
which is co-owned by Meta and Expo.

Changelog:
[Internal] [Changed] - Move expo samples to a service account.

Reviewed By: cipolleschi

Differential Revision: D41533073

fbshipit-source-id: 4745bb35160c401ebb9ce03325bda64726f122dc