[REF] mail: rename mail.notification table

RATIONALE

A bit of history. Link between a message and its recipients has been added
at first mail refactoring towards a Chatter / Discuss feature. It was done
in v7 at d64f3c97 with the base addition of mail notification model (lots
of commits follow that one but that's the first one about notification).

Due to some people thinking that it was unnecessary to keep a model for
notification it has been removed in v9 at 88b8cd05. Notification table was
renamed from mail_notification to mail_message_res_partner_needaction_rel.

It was proven to be a mistake even if those "some people" were warned and
model made its way back to Odoo in v10 at 72dfcae2 . Table name mail_message
_res_partner_needaction_rel was kept to ease migration and backward
compatibility.

It is now time to complete the circle and rename it to mail_notification.

SPECIFICATIONS

Rename ``mail_message_res_partner_needaction_rel`` to ``mail_notification`` .

RIP JEM.

Never forget.

LINKS

Task ID-2477444
Prepares Task ID-2377974 (trace management cleaning task)
Prepares Task ID-2070632 (channel members main task)
Prepares Task ID-2419762 (channel members followup task)
COM PR odoo/odoo#67382
UPG PR odoo/upgrade#2245

Co-Authored-By: Rémy Voet <ryv@odoo.com>
Co-Authored-By: Thibault Delavallée <tde@odoo.com>