[IMP] base: add a default signature on users

When creating a new user, add a default signature if none is given. It
should be a simple one like

```
--
<user_name>
```

Implement it using an editable computed field based on name. That way users
can set it explicitly as void, but changing user's name sets a default one
when it is not set.

Task-2712450 (Mail/Sale: Improve 'Pay Now' notification template)

Part-of: odoo/odoo#82167

odoo/addons/base/models/res_users.py

@@ -14,6 +14,7 @@ import time
 from collections import defaultdict
 from hashlib import sha256
 from itertools import chain, repeat
+from markupsafe import Markup
 
 import decorator
 import pytz
@@ -28,7 +29,7 @@ from odoo.exceptions import AccessDenied, AccessError, UserError, ValidationErro
 from odoo.http import request
 from odoo.osv import expression
 from odoo.service.db import check_super
-from odoo.tools import partition, collections, frozendict, lazy_property
+from odoo.tools import is_html_empty, partition, collections, frozendict, lazy_property
 
 _logger = logging.getLogger(__name__)
 
@@ -285,7 +286,7 @@ class Users(models.Model):
         help="Specify a value only when creating a user or if you're "\
              "changing the user's password, otherwise leave empty. After "\
              "a change of password, the user has to login again.")
-    signature = fields.Html(string="Email Signature", default="")
+    signature = fields.Html(string="Email Signature", compute='_compute_signature', readonly=False, store=True)
     active = fields.Boolean(default=True)
     active_partner = fields.Boolean(related='partner_id.active', readonly=True, string="Partner is Active")
     action_id = fields.Many2one('ir.actions.actions', string='Home Action',
@@ -401,6 +402,11 @@ class Users(models.Model):
             else:
                 user.password = user.new_password
 
+    @api.depends('name')
+    def _compute_signature(self):
+        for user in self.filtered(lambda user: user.name and is_html_empty(user.signature)):
+            user.signature = Markup('<p>--<br />%s</p>') % user['name']
+
     @api.depends('groups_id')
     def _compute_share(self):
         user_group_id = self.env['ir.model.data']._xmlid_to_res_id('base.group_user')