Add support for clusters spanning across multiple Cloudstack API Endpoints

[maxdrib]

What would you like to be added:
Currently, EKS-A accepts one set of credentials for creating a cluster on one Cloudstack environment. The scope of this task is to add support in EKS-A for clusters which can span across multiple Cloudstack endpoints in preflight checking, cluster creation, cluster upgrades, and cluster deletion.

Why is this needed:
The customer has expressed a need for creating clusters across multiple Cloudstack environments/endpoints. Their architecture only enables highly available multi-zone clusters when they are distributed across multiple Cloudstack endpoints, so this feature would enable them to have more resilient and scalable clusters.

[maxdrib]

#2404 modifies the input schema for credentials to be passed to cloudmonkey and CAPC and updates the preflight checks