Feed Metrics with Catalog Monitoring Data Instead

[Amogh-Bharadwaj]

Right now our mirror code has steps in it for collecting data to show on Grafana. We also collect data to store for our native catalog metrics. There is some redundancy here, potentially slowing the flow down a bit.

Instead, we can just use the data we collect for catalog peerdb_stats and provide it to metrics.go.
For example, to get total records at target we could do:

select sum(num_rows) from peerdb_stats.cdc_batch_table;

[heavycrystal]

Grafana metrics removed in #703, therefore this is unnecessary