This patch integrates the new a-c BackgroundSyncManager, which is the
main entry point for interacting with Sync. Behind the scenes, it uses
WorkManager in order to sync configured syncable stores.
Current behaviour:
- sync runs on start, with a slight delay
- sync runs on a schedule few times a day, to lessen the startup sync burden
Also included is a basic UI integration in order to allow user to synchronize
on demand, and monitor sync state.
Grisha Kruglov