[IMP] project: move group inside the view

The goal being to get rid of the `groups_id` feature for backend views

See the related commit in the enterprise part of this pull request.
Here is the commit message for easyness:

In this case, the renaming of the label to "planned date"
is done directly in the base view,
in the community part of this pull request.

It made no sense to change the label from "Dates" to "Date Planned"
when you became a planning user, for all projects.

Either it should be "Planned date" for everyone,
either it should be "Planned" date only for projects using planning.
But not when the user is granted "Planning / User".

It was decided to make this label by default in the base view

Part-of: odoo/odoo#98551

addons/project/views/project_views.xml

@@ -529,7 +529,7 @@
                         <group>
                             <field name="active" invisible="1"/>
                             <field name="user_id" string="Project Manager" widget="many2one_avatar_user" attrs="{'readonly':[('active','=',False)]}" domain="[('share', '=', False)]"/>
-                            <label for="date_start" string="Dates"/>
+                            <label for="date_start" string="Planned Date"/>
                             <div name="dates" class="o_row">
                                 <field name="date_start" widget="daterange" options='{"related_end_date": "date"}'/>
                                 <i class="fa fa-long-arrow-right mx-2 oe_edit_only" aria-label="Arrow icon" title="Arrow"/>