Add new right : See private task assign to my group

[Lainow]

Checklist before requesting a review

Please delete options that are not relevant.

• I have read the CONTRIBUTING document.
• I have performed a self-review of my code.
• I have added tests that prove my fix is effective or that my feature works.
• This change requires a documentation update.

Description

• It fixes !34489
• Here is a brief description of what this PR does

Added a new right so that I can see the private tasks assigned to my group even if I can't see the basic private tasks.

Screenshots (if appropriate):

[cedric-anne]

As discussed IRL, there is no need to add a new right. Private tasks assigned to a group should be visible from users that are part of this group as long as the user has the SEEPRIVATE right.

changes were requested

[Rom1-B]

If a profile has the SEEPRIVATE permission, it can view all private tasks, regardless of assignment. The goal here is to ensure that the user cannot see private tasks (thus without the SEEPRIVATE permission) except those assigned to one of their groups. I don’t have a strong opinion about the new permission, but I believe it adds more clarity to permission management.