[IMP] mass_mailing: add import template for mailing contacts

Currently when user starts using the app and tries to 'import records' from
'Mailing List Contacts', there is no templates available to assist the user.

This commit adds import template for mailing contacts to assist the users
in importing records.

taskID-2763984

closes odoo/odoo#84804

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/mass_mailing/models/mailing_contact.py

@@ -192,3 +192,10 @@ class MassMailingContact(models.Model):
         action['context'] = ctx
 
         return action
+
+    @api.model
+    def get_import_templates(self):
+        return [{
+            'label': _('Import Template for Mailing List Contacts'),
+            'template': '/mass_mailing/static/xls/mailing_contact.xls'
+        }]