Update /stats route to pull data from dagcargo metrics table

[JeffLowe]

needs #1783

It was discovered that the current /stats page "Data Stored" value is too high. Upon further review, it appears to include not only nft, but also web3 data. It needs to match the value that is being reported in the grafana dashboard.

Reference discussion in slack for greater context of need: https://filecoinproject.slack.com/archives/C02BZPRS9HP/p1649282203837359

Tasks

• Adjust query to pull data from the new table.
• Ensure query includes the "week over week change" values needed for the bottom "Data Stored" metric