When the user is updated, their lists on Brevo are overwritten with
the new value: this removes lists set by other products.
Switch to the common lib implementation from `django-lasuite`,
which manages this correctly.
This change was initially proposed by @qbey, but at the time our
deployment did not have a Celery worker running alongside the
backend. Since then, a Celery worker has been deployed, so the
switch to the common lib approach is now safe to adopt.
lebaudantoine
0b4a83c92e