cubicweb #2951067 use the call_services API to retrieve repo stats [validation pending]

We currently add a new method on repo that anyone can call. Call service allows to reach the same result with: - restrict access to manager - do not bloat the Repository class

done in3.19.0
load left0.000
closed by#cc3442054e48 [repo] move repo stats to Service (closes #2951067)
patch[repo] move repo stats to Service [applied]