Feature Request: Add `--force` flag for MoveTables / Workflow completion

[lizztheblizz]

Feature Description

Currently, once movetables has executed switchtraffic, and the original source keyspace gets disconnected for any reason, there is no way to force complete it, and the workflow needs to be manually cleaned up from the sidecar db's.

Adding a --force flag to the complete subcommand could allow the proper cleanup to happen even if the workflow outlives the connection to the source keyspace/database.

Use Case(s)

In scenarios where data is being imported into Vitess from an external keyspace, there can be a prolonged period during which the workflow is left after switchtraffic, but before complete, during which the reverse replication streams are kept running.

Sometimes, at that point, the original source database may end up getting removed without having fully cleaned up the Vitess side workflows. Previously, we would have cleaned up there workflows directly with the workflow delete command, but that is also no longer an option in more recent versions of Vitess.

[mattlord]

Just noting that in this scenario the source keyspace would typically be the one with an active workflow (the reverse one). So with --force that could be left in place and be an orphaned set of vreplication streams. This can be documented as one of many reasons that --force should be used with extreme caution.