Enqueues OpenTofu vendor migration (or rollback) for every stack that matches the given search filter. The mutation is asynchronous. The target argument determines direction: - target=OpenTofu: migrate matching legacy stacks (vendor=Terraform, workflow_tool=OPEN_TOFU) to native OpenTofu vendor. - target=Terraform: roll back previously migrated stacks to the legacy shape. When triggerRun=true, the drain queues a tracked run on each stack after it successfully migrates — useful for validating the new vendor against the customer's existing configuration. Stacks already in the target state, already in the queue, or in conflict are silently skipped.