[bug] single character container names break microvm actors #2800

Micro-VM actors with a one character container name can't start.

We use the container name as the kata container ID, and kata rejects IDs shorter than two characters.

We need to fix this, because it may require a breaking change to fix cleanly, but I think there's a simple solution.

gVisor and Kubernetes both allow these names, so no reason to reject it.