[repo] move repo.gc_stats to Service API (closes #2951068)
We currently have a method on the repo that anyone can call. `call_service`
gives a similar thing, modulo:
* can be restricted access to manager only (thanks to selection on services),
* less unrelated code on the repository class,
* no need to fetch a reference to a repo object from the client side
* (`req._cnx.repo` is not an API and config.repository() is on its way out).
The old way to access this information (repo.gc_stats()) is deprecated.
dn: dc=cubicweb,dc=test
structuralObjectClass: organization
objectClass: dcObject
objectClass: organization
o: cubicweb
dc: cubicweb
dn: ou=People,dc=cubicweb,dc=test
objectClass: organizationalUnit
ou: People
structuralObjectClass: organizationalUnit
dn: ou=Group,dc=cubicweb,dc=test
objectClass: organizationalUnit
ou: Group
dn: cn=logilab,ou=Group,dc=cubicweb,dc=test
gidNumber: 2000
objectClass: posixGroup
objectClass: top
cn: logilab
memberUid: adim
dn: cn=dir,ou=Group,dc=cubicweb,dc=test
gidNumber: 2002
objectClass: posixGroup
objectClass: top
cn: dir
memberUid: adim
memberUid: syt
dn: uid=syt,ou=People,dc=cubicweb,dc=test
loginShell: /bin/bash
objectClass: OpenLDAPperson
objectClass: posixAccount
objectClass: top
objectClass: shadowAccount
cn: Sylvain Thenault
sn: Thenault
shadowMax: 99999
gidNumber: 1004
uid: syt
homeDirectory: /home/syt
shadowFlag: 134538764
uidNumber: 1004
givenName: Sylvain
telephoneNumber: 106
displayName: sthenault
gecos: Sylvain Thenault
mail: sylvain.thenault@logilab.fr
mail: syt@logilab.fr
userPassword: syt
dn: uid=adim,ou=People,dc=cubicweb,dc=test
loginShell: /bin/bash
objectClass: OpenLDAPperson
objectClass: posixAccount
objectClass: top
objectClass: shadowAccount
cn: Adrien Di Mascio
sn: Di Mascio
shadowMax: 99999
gidNumber: 1006
uid: adim
homeDirectory: /home/adim
uidNumber: 1006
givenName: Adrien
telephoneNumber: 109
displayName: adimascio
gecos: Adrien Di Mascio
mail: adim@logilab.fr
mail: adrien.dimascio@logilab.fr
userPassword: adim