Refactor metrics on AVS sync

[dmanc]

Adds avs sync metrics to a Metrics struct and expose updates to such metrics through the metrics library.

Motivation

Solution

Open questions

[samlaf]

LGTM. Left some nit comments.
Also didn't you say you want to start using loki log-derived metrics instead of using explicit metrics?

[dmanc]

LGTM. Left some nit comments. Also didn't you say you want to start using loki log-derived metrics instead of using explicit metrics?

Need to think about it more, there's still value for having some metrics