PURPOSE
Overall cleaning of subscription and exclusion management code from portal.
This code comes mainly from v12 and can now benefit from cleaning and update.
SPECIFICATIONS
In this commit we rename ``mailing.contact.subscription`` model into the
shorter ``mailing.subscription``. This is sufficient to explain the model
purpose. As we plan to add an opt-out model this also allows to have sub
models with suffixes without being too long.
We also rename ``subscription_list_ids`` field on contact model to
``subscription_ids`` as this is shorter and clearer.
Finally the ``mailing_contact_list_rel`` table name that comes from old
implementations (simple m2m table) is renamed to ``mailing_subscription``
to match the model name.
Task-2669037 (Mass Mailing: Refactor js/portal for subscription)
Part-of: odoo/odoo#86084
Thibault Delavallée
b897571b9f