[Remote Store] Add API to check status of remote store sync

**Describe the solution you'd like**
Using this API, use will be able to get the remote store sync status. The status will provide details:
- If remote translog is in-sync
- If remote translog is not in-sync, number of operations it is lagging
- If remote segment store is in-sync
- If remote segment store is not in-sync, number of segments to be uploaded, number of segments to be deleted.

