Is your feature request related to a problem or a Pull Request

Yes. Unable to run k3d cluster create when docker daemon has docker namespaces enabled.

Scope of your request

Do you need...

• a new flag for a command
  • Allow Docker Run With --userns=host on k3d cluster create

Describe the solution you'd like

k3d runs docker with --privileged. With a docker daemon that has user namespaces enabled this will not work unless --userns=host is also passed to docker run. https://docs.docker.com/engine/security/userns-remap/#user-namespace-known-limitations

I propose to add a flag be added to k3d cluster create to allow setting userns.

Describe alternatives you've considered

The package Kind also has the same constraint. However it has addressed this issue by detecting if the docker daemon has namespaces enabled and if so it automatically adds the --userns=host flag. See https://github.com/kubernetes-sigs/kind/blob/5e58a0d40309675774a6df2b25c1947143a03c6c/pkg/cluster/internal/providers/docker/provision.go#L207-L209