PM-6430 - campus leaderboad

[vas3a]

This pull request improves how parent/subgroup relationships are handled in the campus-leaderboard.sql report by unifying the logic for reading group hierarchies. The main enhancement is the introduction of a new group_links common table expression (CTE) to ensure that group relationships are consistently captured from both the GroupMember and _ParentSubGroups tables, making the group tree traversal more robust.

Improvements to group hierarchy handling:

• Added a new group_links CTE that merges parent/subgroup relationships from both groups."GroupMember" and groups."_ParentSubGroups" tables, ensuring no missing links due to incomplete data in either source.
• Updated the group_tree and parent_groups CTEs to use group_links instead of directly querying GroupMember, simplifying and unifying the logic for traversing group hierarchies.