[ENG-10464](https://linear.app/comm/issue/ENG-10464/biggest-risk-handle-target-message-in-messages-table).
I changed the approach to update the column to be a standard column instead of generated. I also don't think it is worth updating `Message.h` entity as this value is not needed at the application level, so I put exactly the same code while inserting to compute `target_message` column.
Depends on D14835