Compatibility attributes and validation

[Kshatrix]

List of attributes:

• Each CAPI provider version (e.g CAPI, CAPA, k0smotron) - exposed by ProviderTemplates, consumed by ClusterTemplates
• K8s version - exposed by ClusterTemplates, consumed by ServiceTemplates

Where to set those attributes:

• On the Templates side we expect those to be defined either in the Template Spec or Chart annotations (similar to the existing approach with providers)
• For ProviderTemplates the exact versions of providers should be defined alongside those providers
• For ProviderTemplates the expected version of CAPI has to be defined
• For ClusterTemplates the exact version of k8s should be defined
• For ClusterTemplates supported versions of providers should be defined with semver constraints
• For ServiceTemplates supported versions of k8s should be defined with semver constraints

How to report those attributes:

• Provider versions are reported in the Management object status based on versions defined in ProviderTemplates of enabled providers
• K8s version is reported in the ManagedCluster object status based on k8s version defined in ClusterTemplate

Compatibility enforcement:

• Semver-based
• All described attributes are optional: no attributes -> no validation
• If a ClusterTemplate and HMC are incompatible, ManagedCluster creation/upgrade from/to this template should be forbidden
• If a ServiceTemplate and ManagedCluster are incompatible, adding this template to the ManagedCluster should be forbidden

Impact on HMC upgrade:
If we have existing ManagedClusters and upgrading HMC would lead to incompatibility with at least one enabled provider, HMC upgrade should be forbidden by admission-controller.

Related issues:

• API changes to support compatibility attributes #354
• Compatibility attributes: implement enforcement #400
• Compatibility attributes: document changes #401