[services][feature-flags] Query the db
The final diff about accessing the database.
Depends on D6856
Test Plan: Create some dummy data in the db. Query the db, log the result and verify that the parsed data is correct.
Reviewers: michal, bartek, jon, varun
Reviewed By: bartek
Subscribers: ashoat, atul
Differential Revision: https://phab.comm.dev/D6857