[FIX] crm: apply threshold for leads/opportunities in merge wizard

Purpose of this task is to prevent merging of opportunities when
a regular (non super) user selects more than five records.

This commit limits total number of recorrds to be merged, up to maximum
five leads / opportunities for non superuser environment, and raises a
UserError otherwise explaining the threshold limit.

closes odoo/odoo#55024

Task-id: 2256126
X-original-commit: c25d7654f250c888cea84c20af16b2a32cc5b365
Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/crm/models/crm_lead.py

@@ -969,6 +969,9 @@ class Lead(models.Model):
         if len(self.ids) <= 1:
             raise UserError(_('Please select more than one element (lead or opportunity) from the list view.'))
 
+        if len(self.ids) > 5 and not self.env.is_superuser():
+            raise UserError(_("To prevent data loss, Leads and Opportunities can only be merged by groups of 5."))
+
         opportunities = self._sort_by_confidence_level(reverse=True)
 
         # get SORTED recordset of head and tail, and complete list