Follow-up to #2687843: Add back incremental migrations through the UI
Problem/Motivation
Follow-up to #2683421: Remove incremental and rollback options from the UI (and add them back when they are more stable) which removes both the rollback and incremental options since they were untested and had several significant bugs. Unlike the incremental migration feature, rollback can probably be considered an additional feature and not necessarily block a stable Migrate UI.
Proposed resolution
Add back rollback migration support to the UI, with test coverage. Consider refactoring the form and batch process so the logic for it is not entangled with the initial migration and the rollback option.
Remaining tasks
TBD
User interface changes
In #2683421: Remove incremental and rollback options from the UI (and add them back when they are more stable), the UI disallows both incremental migrations and rollbacks. Here is what it looked like before that:
We might want to either reimplement that, or change it.
API changes
Depends on the solution.
Data model changes
None
