[FIX] website: multi website - auto public user

Before this commit
When user was in company A and try to create a second website for company B an
error was raised, because the search from user in company A don't find a public
user in company B and the same default user (public-user@company-B.com) was
created again before to be catched and raised by the sql contraint login_key.

Now we use '-' instead of '_' to avoid parser of email to detect it as invalid

After this commit, we don't have anymore the error:
    - 'You can not have two users with the same login!'
 or - 'Login must be a valid email address'

opw-1891315

closes odoo/odoo#27873

addons/website/models/res_company.py

@@ -20,7 +20,8 @@ class Company(models.Model):
     @api.multi
     def _get_public_user(self):
         self.ensure_one()
-        public_users = self.env.ref('base.group_public').with_context(active_test=False).users
+        # We need sudo to be able to see public users from others companies too
+        public_users = self.env.ref('base.group_public').sudo().with_context(active_test=False).users
         public_users_for_website = public_users.filtered(lambda user: user.company_id == self)
 
         if public_users_for_website:
@@ -28,7 +29,7 @@ class Company(models.Model):
         else:
             return self.env.ref('base.public_user').sudo().copy({
                 'name': 'Public user for %s' % self.name,
-                'login': 'public_user@company_%s.com' % self.id,
+                'login': 'public-user@company-%s.com' % self.id,
                 'company_id': self.id,
                 'company_ids': [(6, 0, [self.id])],
             })