[native] Fetch and parse feature flags response

Summary:
Fetch a config, parse, and use in a state.

Depends on D6948

Test Plan: Added a console log to check if the state is set correctly after successful call to feature flags service.

Reviewers: kamil, bartek, inka

Reviewed By: bartek

Subscribers: ashoat, atul

Differential Revision: https://phab.comm.dev/D6949