[IMP] {fetch}mail, google_gmail, microsoft_outlook: merge fetchmail into mail

The `fetchmail` module is build on top of the `mail` module and enables
the incoming email capabilities. However, using the `mail` without
incoming email server is not a good use case.

This commit merges the `fetchmail` moudule into `mail` and lessens the module
complexity, along with adapting the xml/external ids in the dependent modules.

task-2797458

closes odoo/odoo#94143

Related: odoo/upgrade#3615
Related: odoo/enterprise#28659
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/google_gmail/__manifest__.py

@@ -7,7 +7,6 @@
     "category": "Hidden",
     "description": "Gmail support for incoming / outgoing mail servers",
     "depends": [
-        "fetchmail",
         "mail",
     ],
     "data": [

addons/google_gmail/views/fetchmail_server_views.xml

@@ -4,7 +4,7 @@
         <field name="name">fetchmail.server.view.form.inherit.gmail</field>
         <field name="model">fetchmail.server</field>
         <field name="priority">100</field>
-        <field name="inherit_id" ref="fetchmail.view_email_server_form"/>
+        <field name="inherit_id" ref="mail.view_email_server_form"/>
         <field name="arch" type="xml">
             <field name="user" position="after">
                 <field name="google_gmail_uri" invisible="1"/>