[Feature]: Add `Blob Count` column on blob stores admin view.

[visit1985]

Problem or use case

As an admin, I would like to have an overview on my different blob stores usage.

Proposed behavior

A Blob Count column on the Blob Stores admin view would help admins to get an overview on their different stores. It would also help a lot to have a similar Asset Count column on the Repositories admin view to narrow it down to individual repositories in a blob store.

Affected area

Admin UI

Nexus or official protocol reference

The Blob Stores column is available in Nexus.

Alternatives considered

No response