Delete challenges in the cluster after the directory got deleted

[spq]

When deleting a challenge or renaming it, it can happen that one forgets to delete the challenge in the cluster before doing so.
It is not clear to me how to delete a challenge from the cluster in this case.
A command like kctf chal delete --name=xxx would be a nice way to allow this.

[terjanq]

Renaming challenge name in metadata also cause some caching problems where the name of the container changed, but the deployed DNS entries were still under the old name. I guess the docker image for external DNS didn't force rebuild?