Fix: Planner role unable to read_code/download_code on private projects with default permissions

What does this MR do and why?

Adjusts permissions for the Planner role in private projects to grant code access while restricting analytics and merge request creation.

Closes #550282 (closed)

Changes

This MR updates the Planner role permissions in private projects:

Enabled:

• :read_code - Planners can view code in private projects
• :download_code - Planners can clone/download code from private projects

Prevented:

• :read_code_review_analytics - Planners cannot access Code Review Analytics
• :create_merge_request_in - Planners cannot create merge requests in private projects

Screenshots

After	Before

Steps to verify

1. Create a private project
2. Invite user as planner
3. Log in as a planner user
4. Check if you can read and download it

Related to #550282 (closed)