[FIX] mass_mailing: allow to quick create a mass_mailing

_rec_name in mass mailing is source_id which is an integer, it does not accept
a char value.
Instead specify the `name` value, which will create a utm.source.

Closes odoo#13765

Author: danimaribeiro

addons/mass_mailing/models/mass_mailing.py

@@ -424,6 +424,12 @@ def _onchange_model_and_list(self):
     # Technical stuff
     #------------------------------------------------------
 
+    @api.model
+    def name_create(self, name):
+        """ _rec_name is source_id, creates a utm.source instead """
+        mass_mailing = self.create({'name': name})
+        return mass_mailing.name_get()[0]
+
     @api.multi
     def copy(self, default=None):
         self.ensure_one()