Externalise parameters for more flexible kubernetes deployment.

[iwinoto]

Aim:
Allows user a choice of image repo and deploy the demo to choice of kube clusters.

Summary of changes:
Modified the kubernetes/ci.sh and associated YAMLs to externalise parameters for

• image repos (docker namespace or IBM Cloud container registry region and namespace)
• IBM Cloud IKS regions
• IBM Cloud IKS cluster
• kube namespaces
• ingress subdomain (Ingress subdomain is typically defined by kube cluster provider, although cluster owner can usually specify a custom domain.)

Testing:
Only tested with IKS and docker.hub. Partially tested with IBM Cloud container registry.

Known issues:
None