Make real subscription records for contact / list link, in order to have values
for inner model fields and ease their management / update / removal. It is
better than relying on m2m commands.
Also harmonize some xml ids names to ease future changes.
Task-2702607
Part-of: odoo/odoo#135299
Purpose is to ease tracking of data and demo through versions by avoiding
the usage of huge file. Instead split data and demo / main model.
Task-2702607
Part-of: odoo/odoo#135299