[FIX] im_livechat_mail_bot: import user model file

Otherwise you **might** ran into issues with missing selection field key.

Commit linked to task ID 1887949.

addons/im_livechat_mail_bot/models/__init__.py

@@ -2,3 +2,4 @@
 # Part of Odoo. See LICENSE file for full copyright and licensing details.
 
 from . import mail_bot
+from . import res_users

addons/im_livechat_mail_bot/models/res_users.py

@@ -3,10 +3,10 @@
 
 from odoo import models, fields
 
+
 class Users(models.Model):
     _inherit = 'res.users'
     odoobot_state = fields.Selection(
         selection_add=[
             ('onboarding_canned', 'Onboarding canned'),
         ])
-