User name changes

[chibenwa]

For all LDAP users
if local part of email address is not equal to the uid
and if @domain.tld mailboxes are not empty on james side
then trigger a data migration from @domain.tld to the new mail address

With such a schema users may not change name twice but thats the only way I found to do this based on states, without the actual rename event.

Can run nightly.

Cc @guimard @quantranhong1999

[chibenwa]

Harder: on MU the uid is not the local part of the email.
It would not be as easy.
It's likely we would need to store some data on tmail: we are likely in for another extension...