Cleanup Sync.kt to provide only WorkManager based sync apis.

[aditya-07]

Describe the Issue Presently there are a lot of overlapping ways/apis in the Sync.kt available for the developer application to sync data with the remote server.

Expected changes:

1. It should have a simple interface with two api : One for immediate Onetime sync and other for periodic sync.
2. The developer app should be able to listen-in to the state of ongoing sync via Flow.

Would you like to work on the issue?

[Tarun-Bhardwaj]

@jingtang10 do you think fixing this issue would impact #1469?

[jingtang10]

Closing this as this was addressed in #1578.

@aditya-07 please feel free to reopen if you think this is not sufficiently addressed. thanks for creating this issue!