Check for Lotus API sync status

[ognots]

Snapshots will start when connected to unsynced lotus node APIs, and then eventually fail.
As part of node selection logic, filecoin-chain-archiver should check if the lotus node is synced before acquiring a lock and proceeding with an export.
The problem caused by this issue is compounded, because we need to reset lotus nodes every 3 days on mainnet. While they are resyncing after reset, jobs try to run on them, and fail.