Root establishment is not handled correctly

When setting an establishment as the root one, it’s copied under the root, while after reading SupAnn and official examples it appears that it’s supposed to be copied into the root node itself, for example:

dn: dc=univ-paris1,dc=fr
objectClass: dcObject
objectClass: organization
objectClass: eduOrg
objectClass: supannOrg
dc: univ-paris1
o: UP1
description: Université Paris 1 Panthéon-Sorbonne
eduOrgLegalName: Université Paris 1 Panthéon-Sorbonne
eduOrgHomePageURI: http://www.univ-paris1.fr
eduOrgWhitePagesURI: http://annuaire.univ-paris1.fr
supannEtablissement: {UAI}0751717J

Source: https://services.renater.fr/documentation/supann/supann2018/recommandations2018/structures/etab

We should modify our code to do this and see if it does not cause any problem.

Then we’ll need to offer a migration path to users.