Support environment variables defined in Knative manifests when spawning MicroVMs

[ustiugov]

Currently, ctriface/ doesn't pick up environment variables from the knative manifests. Firecracker-containerd supports it at a the container creation time as a runtime argument to the corresponding API call.

Example:

	container, err := o.client.NewContainer(
		ctx,
		vmID,
		containerd.WithSnapshotter(o.snapshotter),
		containerd.WithNewSnapshot(vmID, *vm.Image),
		containerd.WithNewSpec(
			oci.WithEnv([]string{fmt.Sprintf("%s=%s", minioEnvVarKey, o.minioAddress)}),
			oci.WithImageConfig(*vm.Image),
			firecrackeroci.WithVMID(vmID),
			firecrackeroci.WithVMNetwork,
		),

The use case is to enable and disable tracing when running vHive with Firecracker MicroVMs. As of now, this must be hardcoded in each function image.