PURPOSE
Reorganize and lint mail.channel code. Purpose is to ease future modifications
linked to groups and channels in mail / Discuss.
SPECIFICATIONS
Cleanup a bit mail addon by moving menu definitions in their own file
according to guidelines.
LINKS
Prepares Task ID-2070632 (Discuss channel task)
Prepares Task ID-2419762 (SM channel task)
COM PR odoo/odoo#64862
Purpose is to lessen size of technical "Email" menu and move some
discuss menu entries in their own menu. It will be the new first menu
entry in technical, before Emails that is more technical.
Some menu items are moved in this new menu, notably followers, messages
or mail blacklist.
Emails menu is also reordered, to have notably all channels related
entries together, ...
Task 2118599
PR #39460
Thibault Delavallée