Jailing should be available without calling firecracker-containerd's APIs

While Firecracker is [recommending customers to use a jailer in production](https://github.com/firecracker-microvm/firecracker/blob/master/docs/prod-host-setup.md);

> Using Jailer in a production Firecracker deployment is highly recommended, as it provides additional security boundaries for the microVM.

Our internal, implicit CreateVM call doesn't use a jailer.

https://github.com/firecracker-microvm/firecracker-containerd/blob/4d1bab34e9beba70165fe408a07eb512c21a99d7/runtime/service.go#L355-L359

In other words, customers need to use CreateVM explicitly to enable a jailer.