In this commit, we add a new feature allowing project tasks to be dispatched automatically based on:
- The roles we have defined in the tasks of a project template
- And a role-to-users mapping showing up when creating a new project from a project template

This feature enhances task management by ensuring that tasks are assigned to the appropriate team members according to their roles, improving efficiency and clarity in project execution.

More precisely, we add a new model: 'Project Roles' that we can link to tasks templates (as long as they belong to a project template).
We can link multiples roles to a single task template, and a role can be linked to different tasks too. A menu item for 'Project Roles' has been added.

When creating a new project from a project template, the user can select in the wizard which users are going to be assigned to the task if some roles match.
This mapping is only visible if at least one role has been defined in any task of the project template, and the available roles in that mapping are only the roles defined in those tasks.
If multiple roles match, all the users matching those roles will be assigned to the task. If a task already contains some assignees, they will not be overridden but the matching users will be added to the existing assignees.

task-4700746

Before this commit, when creating a new project from a template, the 'partner_id' field
was being removed from the values given to 'action_create_from_template()', even if
it was explicitly set in the 'values' parameters we want the new project to have.
For instance when specifying the 'Customer' field from the project creation from template wizard,
it was not being taken into account, and the new project was created without a partner.
Same when a product is configured to generate a project from a template, the partner was not set
on the new project. We adapt the copy method of project to do so.
We also make projects billable by default and remove some 'default_allow_billable' contexts as it's not useful anymore, and we adapt tests accordingly.