[ADD] hr: add activity mixin on employees

Scheduling activities on employees is something people working in human
resources seem to do sometimes.

Closes #19483 .

addons/hr/models/hr.py

@@ -95,7 +95,7 @@ class Employee(models.Model):
     _name = "hr.employee"
     _description = "Employee"
     _order = 'name'
-    _inherit = ['mail.thread', 'resource.mixin']
+    _inherit = ['mail.thread', 'mail.activity.mixin', 'resource.mixin']
 
     _mail_post_access = 'read'
 

addons/hr/views/hr_views.xml

@@ -121,6 +121,7 @@
                     </sheet>
                     <div class="oe_chatter">
                         <field name="message_follower_ids" widget="mail_followers" groups="base.group_user"/>
+                        <field name="activity_ids" widget="mail_activity"/>
                         <field name="message_ids" widget="mail_thread"/>
                     </div>
                 </form>