[IMP] hr: make default calendar required

Through the HR setting, you can set the default
calendar for employee in the company. This field
is not required, and not setting it can be annoying
on employee creation.
This commit makes the field required only on the UI,
as default calendar is generated on company creation,
we can not set the required flag on the model.

Task-1827986

addons/hr/views/res_config_settings_views.xml

@@ -21,7 +21,7 @@
                                 </div>
                                 <div class="content-group">
                                     <div class="mt16">
-                                        <field name="resource_calendar_id"
+                                        <field name="resource_calendar_id" required="1"
                                             class="o_light_label"
                                             domain="[('company_id', '=', company_id)]"
                                             context="{'default_company_id': company_id}"/>