cubicweb #2497108 [ldapuser source] provide a troubleshooting tool [validation pending]

sometimes things get messed up and we get several eids for one extid (for causes such à upstream ldap changes or in-the-field hard-to-track reasons)

we need a tool to list the doublons and eventually merge them back into one entity

done in3.15.5
load left0.000
closed by#56d9eb013feb [misc/scripts] a slightly experimental script to help repair LDAPUser cwusers suffering from split-brainite (closes #2497108)