[Feat]: sync/mirroring status API / UI / metrics needed

[mikemccracken]

Is your feature request related to a problem? Please describe.

I am migrating from one zot instance to another, I have sync configured from the old to the new instance, with onDemand: false.

I want to check that a sync has completed against the old instance before turning sync off.
It looks like the only way to confirm this is to look in the logs for finished syncing all repositories.

It would be very useful to have more visibility without needing access to logs, into whether there is an active sync happening, how many images were synced so far / in total, when the next scheduled sync is, etc.

Ideally there would be UI for this, but even starting with exposing it as a metric for the metrics endpoint would be good.

This would be even more useful for other mirroring use cases, not just the one-time sync I am doing.

Describe the solution you'd like

No response

Describe alternatives you've considered

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Additional context

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