Ensure DB migration 7.9->8.9 on SQL Server is performant after Hardening on big dataset

During the 8.9 Hardening Sprint, a few DB Migration changes were performed (more details here) 

We need to make sure that these changes have not broken the expected performance for the 7.9 to 8.9 Migration path in SQL Server.

The goal is to validate that performance did not decrease for a big dataset (1.2To), and that it is still within 48 hours.

Results:

• Migration 7.9->8.9 took 16h for a 1.2To dataset.
• Test database is an AW RDS db.m5.xlarge (4vCPUs, 16GiB memory), with 10.000 provisioned IOPS