wkdev-update: Delete container before recreating

[ptomato]

I recently ran out of disk space while running wkdev-update and had to manually delete the existing container image with podman rmi before creating a new one. The containers are tens of gigabytes, so it'd be good for wkdev-update to first delete the old container.

(Alternatively, if we don't want to delete first by default, we could instead wait until the process fails due to disk space, then delete the old container and retry)

[nikolaszimmermann]

But if the creation fails for some reason, wouldn't you want to keep the old one? Not sure if deleting before is wise...
Maybe we could warn instead of there is e.g. less than 20 GB disk space available?