Add indexes on account payment models

The fields where the indexes are added are used in searches in
account_payment_order, which becomes really slow when a database have
many lines.

account_payment_partner/models/account_move_line.py

@@ -11,5 +11,6 @@ class AccountMoveLine(models.Model):
         'account.payment.mode',
         string='Payment Mode',
         domain="[('company_id', '=', company_id)]",
-        ondelete='restrict'
+        ondelete='restrict',
+        index=True,
     )