Capture state size over time

[kasteph]

Description

Create a graph of the Filecoin chain state size over time. If stats for the entire history of Filecoin mainnet is expected, then we'd need to run this against an existing full node or run a backfill process.

Acceptance criteria

• A new task that calculates the size of the chain every N epochs
• A schema for a table containing state stats

Where to begin

• lotus-shed stateroot stats cmd