Add sharding key not null constraint on zentao_tracker_data

What does this MR do and why?

This MR adds not null constraint to zentao_tracker_data sharding key columns to ensure every record has one. Please note that:

1. All new records have sharding key set as part of !189933 (merged)
2. All old records were backfilled via !192824 (merged)
3. Model sharding key presence validation is already present

Migration output

Up

main: == [advisory_lock_connection] object_id: 143920, pg_backend_pid: 20344
main: == 20250820140416 AddMultiColumnNotNullConstraintToZentaoTrackerData: migrating 
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- execute("ALTER TABLE zentao_tracker_data\nADD CONSTRAINT check_fcff5b4d60\nCHECK ( num_nonnulls(group_id, organization_id, project_id) = 1 )")
main:    -> 0.0024s
main: == 20250820140416 AddMultiColumnNotNullConstraintToZentaoTrackerData: migrated (0.0554s) 

Down

main: == [advisory_lock_connection] object_id: 144280, pg_backend_pid: 20166
main: == 20250820140416 AddMultiColumnNotNullConstraintToZentaoTrackerData: reverting 
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- transaction_open?(nil)
main:    -> 0.0000s
main: -- execute("            ALTER TABLE zentao_tracker_data\n            DROP CONSTRAINT IF EXISTS check_fcff5b4d60\n")
main:    -> 0.0024s
main: == 20250820140416 AddMultiColumnNotNullConstraintToZentaoTrackerData: reverted (0.0474s) 

main: == [advisory_lock_connection] object_id: 144280, pg_backend_pid: 20166

References

#560350 (closed)

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Go to admin settings - create instance wide zentao integration -- verify it's active and created successfully
2. Check zentao_tracker_data table -- verify integration is created for each of the instance's group and project and each record has a sharding key
3. Create a group and a project while having active zentao integration
4. Verify group/project successfully created
5. For a group -- go to integration settings and setup group specific zentao integration
6. Verify it's updated successfully, sharding key is present in the database

MR acceptance checklist

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