Add k8ssandra to the demos

[philkuz]

Is your feature request related to a problem? Please describe.
k8ssandra is a great way to demo cassandra data. We should add it to the demos and our release test process.
https://docs-v2.k8ssandra.io/install/local/single-cluster-helm/

Describe the solution you'd like

px demo deploy k8ssandra

[ddelnano]

I've been working on this for the Cassandra Town hall I'll be presenting at. The difficult part is allowing the px demo command to support the more complex k8ssandra (requires installing crds before hand or integrating with helm).

[ddelnano]

With #1376 merged the demo is fully functional. We just need to upload the demo manifests to the production gcs bucket and release the px cli for this to be complete.