[MERGE] project,hr_timesheet: simplify the user onboarding

This merge provides many little changes to improve the usability
and the onboarding of users in project and timesheet
applications.
This mostly contains labels renaming, restruration of views, ...
but some new mecanism appears like the "ghost kanban examples",
and improvements of the kanban examples modal.

Task-1893021

closes odoo/odoo#28461