[IMP] project: task stage improvement in the project app

This commit removes the tooltip of the `fold` field because
the second part is no longer true and the first part does not
provide any added value.
It also makes `project_ids` field required in the form view of
Task Stage model (`project.task.type`) to force the user to link
his new stage to a project. Otherwise, the stage won't ever be
visible anywhere in the interface. Indeed, stages not holding
tasks are hidden in cross-projects views.

task-3251621

closes odoo/odoo#121154

Signed-off-by: Xavier Bol (xbo) <xbo@odoo.com>

addons/project/models/project_task_type.py

@@ -27,8 +27,7 @@ class ProjectTaskType(models.Model):
         string='Email Template',
         domain=[('model', '=', 'project.task')],
         help="If set, an email will be automatically sent to the customer when the task reaches this stage.")
-    fold = fields.Boolean(string='Folded in Kanban',
-        help='If enabled, this stage will be displayed as folded in the Kanban view of your tasks. Tasks in a folded stage are considered as closed.')
+    fold = fields.Boolean(string='Folded in Kanban')
     rating_template_id = fields.Many2one(
         'mail.template',
         string='Rating Email Template',

addons/project/views/project_task_type_views.xml

@@ -36,7 +36,7 @@
                             </group>
                             <group>
                                 <field name="fold"/>
-                                <field name="project_ids" widget="many2many_tags" options="{'color_field': 'color'}"/>
+                                <field name="project_ids" required="1" widget="many2many_tags" options="{'color_field': 'color'}"/>
                             </group>
                         </group>
                     </sheet>