fix(user): clear caches when deleting user group

[Cynthia-0203]

What this PR does / Why we need it:

Clear stale user-group and group-role caches when deleting a user group to prevent users from retaining outdated project permissions.

What is changed and how it works?

• Query the user group members before deletion.
• Delete the user group from the database.
• Clear the gid_role_<group_id> cache.
• Clear each member’s user_group_<uid> cache.
• Perform delayed cache deletion after 2 seconds to prevent stale cache recreation.

Does this PR introduce a user-facing change?

• API change
• database schema change
• upgrade assistant change
• change in non-functional attributes such as efficiency or availability
• fix of a previous issue

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This change is