ewaol-distro: Add K3S container orchestration support for EWAOL images

K3S is a lightweight Kubernetes distribution designed for orchestrating
containerised edge workloads.

This patch adds the K3S-server package from meta-virtualization to EWAOL build
targets, and adds a systemd service override to stop K3S orchestration and all
associated containers on device shutdown via a modified version of the
Rancher-provided k3s-killall.sh script.

Also include the xt-statistic kernel module required by K3S for iptables
configuration.

Issue-Id: SCM-2365
Signed-off-by: Richard Neill <richard.neill@arm.com>
Change-Id: Ic649cbe74a3ab56a56ab6c296160d942dd597bab