Purpose
=======
Less secured apps are no longer supported by google, therefore, we need
to transition to the OAuth2 authentication system.
Specifications
==============
1. User will need to fill their Gmail API credentials in the main
settings page
2. Then, in the incoming / outgoing mail server form view, they will
need to tick the Gmail support checkbox
3. A link will be available to be redirected to Gmail and accept the
permission
4. The user can now copy / paste the authorization code in Odoo, set
his email as "login" and then send / receive emails with Gmail
Task-2170676
closesodoo/odoo#83424
X-original-commit: ff223afc5300b2421b8ce935bb468f503c938c5d
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>