`isUnique` was passed to TypeORM's column creation API resulting in
double index creation because it's already done via the decorator and
then in `WorkspaceMigrationIndexFactory`
It would be interesting to move it at this field level in a later step,
which is why I also fixed `CompositeColumnActionFactory` to pass
isUnique on the correct columns, even though it's being ignored later on
f3fe3abf71