Explore CAPI ClusterClass as an alternative to Base Clusters

[bcle]

ClusterClass is CAPI's experimental support for cluster templates. There was a recent Hackathon demonstrating the virtues of ClusterClass. They include:

1. Creating workload clusters with slight customizations relative to a set of templates
2. (I believe, although haven't verified) The ability to update one template, and propagate changes to all clusters created from that template

(2) duplicates what base clusters currently do (linked updates)
(1) is an improvement over base clusters, which don't currently support overrides (see #110)

Aha! Link: https://pf9.aha.io/features/ARLON-297

[bcle]

My recent interactions with ClusterClass indicate that it's still not mature in some scenarios (e.g. EKS and MachinePools), so moving out of 0.10.0 for now.

[cruizen]

My recent interactions with ClusterClass indicate that it's still not mature in some scenarios (e.g. EKS and MachinePools), so moving out of 0.10.0 for now.

@bcle Shall we move this from 0.11 project/ milestone to backlog?