[FIX] mail: Default assignee list for activity types is cut off

Step to reproduce the bug:
- Have more than 100 users
- Have CRM installed
- Go to CRM > Configuration > Activity Types > Create

Bug:
The Default User selection only displays the 100 first users

opw:2330339

closes odoo/odoo#57455

X-original-commit: 75eef2506ba415d3e2be5ac3c14029bba3ed26d0
Signed-off-by: Nicolas Martinelli (nim) <nim@odoo.com>

addons/mail/views/mail_activity_views.xml

@@ -15,7 +15,7 @@
                         <group name="activity_details">
                             <field name="active" invisible="1"/>
                             <field name="category"/>
-                            <field name="default_user_id" widget="selection" domain="[('share', '=', False)]"/>
+                            <field name="default_user_id" options="{'no_create': True, 'no_edit': True}" domain="[('share', '=', False)]"/>
                             <field name="res_model_id" groups="base.group_no_one"/>
                             <field name="res_model_change" invisible="1"/>
                             <field name="initial_res_model_id" invisible="1"/>