support insert mode in the migration worker
support insert mode in the migration worker

set the MIGRATE_MODE env varialbe to `i` to use insert mode and speed
things.

Beit-Hatfutsot/dbs-back,Beit-Hatfutsot/dbs-back,Beit-Hatfutsot/dbs-back,Beit-Hatfutsot/dbs-back