[FIX] hr: add private contact to employee's followers

When creating an employee with a private contact,
the contact will not be automatically added to the employee's followers.

The desired behavior is that the contact is added
to the followers even if it has a private address.
Commit: 8760a4d0

However, this behavior will not be possible because
adding a contact with a private address is forbidden.
Commit: 20536e1b

Solution:
The solution is to use the private method `_message_subscribe`.
This is not a problem in the business case.
Indeed, the people who have access to the employee's file
also have access to the private contacts.
Moreover, the access rights of the public method `message_subscribe`
do not concern this business case.

opw-3249646

closes odoo/odoo#118779

X-original-commit: b06857afa371d2164f1f5ec402a6074a237d8230
Signed-off-by: Kevin Baptiste <kba@odoo.com>

addons/hr/models/hr_employee.py

@@ -331,7 +331,6 @@ class HrEmployeePrivate(models.Model):
         employees = super().create(vals_list)
         if self.env.context.get('salary_simulation'):
             return employees
-        employees.message_subscribe(employees.address_home_id.ids)
         employee_departments = employees.department_id
         if employee_departments:
             self.env['mail.channel'].sudo().search([
@@ -340,6 +339,7 @@ class HrEmployeePrivate(models.Model):
         onboarding_notes_bodies = {}
         hr_root_menu = self.env.ref('hr.menu_hr_root')
         for employee in employees:
+            employee._message_subscribe(employee.address_home_id.ids)
             # Launch onboarding plans
             url = '/web#%s' % url_encode({
                 'action': 'hr.plan_wizard_action',
@@ -360,7 +360,8 @@ class HrEmployeePrivate(models.Model):
             if account_id:
                 self.env['res.partner.bank'].browse(account_id).partner_id = vals['address_home_id']
             self.message_unsubscribe(self.address_home_id.ids)
-            self.message_subscribe([vals['address_home_id']])
+            if vals['address_home_id']:
+                self._message_subscribe([vals['address_home_id']])
         if vals.get('user_id'):
             # Update the profile pictures with user, except if provided 
             vals.update(self._sync_user(self.env['res.users'].browse(vals['user_id']),