There is a simple connection between tx_ter_extensiondetails and tx_ter_extensions (extensionuid field), but both tables always need to be kept in sync. This is unnecessary overhead. For this reason, all data is now moved into tx_ter_extensions (which will later be moved into tx_terfe2_domain_model_version).
After adding the new fields to the database table "tx_ter_extensions", A onetime CLI command "ter:migrateextensiondetails" is executed and syncs all existing data into the main "tx_ter_extensions".
"tx_ter_extensiondetails" can be dropped after the migration, as it is not used anymore at all.