feat: KWASM_DIR configurable

[trutx]

In this PR:

• Make the KWASM_DIR value configurable via env vars
• Bump containerd/runwasi runtimes to v0.4.0
• Rely on $PATH to discover the systemctl binary location

The motivation of this PR is to make the script also able to provision GKE nodes using the cos_containerd image. Such image has many partitions mounted with ro or noexec or both. For example, the default /opt/kwasm dir would land on

/dev/mapper/vroot on / type ext2 (ro,relatime)

so the dir could never be created. However there are other partitions where users can read and execute. This PR adds the ability to pass in a custom KWASM_DIR value where things will be installed in the hosts.

I'm also bumping some versions to the latest release and also relying on the $PATH env var to discover the systemctl location rather than passing a full path. Turns out in nodes running cos_containerd the binary lives in /usr/bin/systemctl. In this decision I'm assuming $PATH is always correctly set in RKE and any other K8s distribution. I think it's a pretty safe assumption to make but happy to code a specific GKE case if needed.