[IMP] mail: mark first welcome message as read for the admin

Actually, We don't want to distract the admin with an unnecessary notification
on General Channel. The main focus should be on odoobot's tour, not on the
general channel's welcome message. And it is also not a good idea to remove the
general channel as it would reduce the discoverability of the feature.

So, we are marking the first message as read for at least admin user.
therefore admin can not distract over unnecessary welcome notification and
focus more on the rest of the functionality.

Task : 2442023

closes odoo/odoo#66010

X-original-commit: 069923e53fcb93c4cf0a0715d500d23525aafbe7
Signed-off-by: Sébastien Theys (seb) <seb@odoo.com>

addons/mail/data/mail_channel_data.xml

@@ -4,7 +4,6 @@
 
         <record model="mail.channel" id="channel_all_employees">
             <field name="name">general</field>
-            <field name="group_ids" eval="[Command.link(ref('base.group_user'))]"/>
             <field name="description">General announcements for all employees.</field>
         </record>
 
@@ -19,5 +18,16 @@
             <field name="body"><![CDATA[<p>Welcome to the #general channel.</p>
             <p>This channel is accessible to all users to <b>easily share company information</b>.</p>]]></field>
         </record>
+
+        <record model="mail.channel.partner" id="channel_partner_general_channel_for_admin">
+            <field name="partner_id" ref="base.partner_admin"/>
+            <field name="channel_id" ref="mail.channel_all_employees"/>
+            <field name="fetched_message_id" ref="mail.module_install_notification"/>
+            <field name="seen_message_id" ref="mail.module_install_notification"/>
+        </record>
+
+        <record model="mail.channel" id="mail.channel_all_employees">
+            <field name="group_ids" eval="[Command.link(ref('base.group_user'))]"/>
+        </record>
     </data>
 </odoo>