Instrument piece adds to gage multi-copy success rate

[BigLep]

Done Criteria

1. We can see what proportion of multicopy "piece additions" succeed
2. In the case where they fail, we have visibility into what step failed and which SP failed

Why Important

As identified during ORR, we are lacking visbility into how successful we are the multi-copy golden path. Filecoin Pin is a place we can actually measure this.

Notes

1. Before picking this up, lets do a bit more desing about the specific metric names/definitions emitted to make sure we don't overengineer and are on the same page.