Truncating the Migration List itsself is easy. You only have to create a snapshot of the current database state (after correctly reseeding first).
php bin/cake.php bake migration_snapshot InitDb
Then you should check if it did it correctly. You can delete all other migrations and run the new migration. If the schema dump is the same it worked.
Be sure to check data update queries and redo them in the new unified migration if possible/necessary.
Major changes include the swap from AbstractMigration to BaseMigration and the same with Seeds.
Be sure to check your seeds and migrations for any outputs. The new BaseMigration or BaseSeed use $this→getIo→out() instead of $this→getOutput→writeln().
Commands have also changed entirely from
php bin/cake.php migrations seed
to
php bin/cake.php seeds run
The default Namespace Separator in DokuWiki seems to be : which I personally find a bit confusing. Luckily there is a configuration to allow / to be used as a Namespace Separator which makes more sense.