Make this repo manageable

We already noticed that there is an issue with the structure of this repo in:

• https://github.com/SovereignCloudStack/cluster-stacks/issues/56
• https://github.com/SovereignCloudStack/cluster-stacks/issues/96
• https://github.com/SovereignCloudStack/cluster-stacks/issues/101

What those have in common and what @paulphys @chess-knight and @mxmxchere have identified as a key-issue is an "artificial" dependency between the cluster-class and the kubernetes version.

Clusterclass is meant to be a template for Cluster-API and cluster-api-provider-openstack resources supporting multiple kubernetes versions. The kubernetes version therefore resides in the cluster-resource and not in the cluster-class.

We should stop putting the kubernetes version inside the ClusterClass name. If we do that, we have the problem that the cso will no longer work.

How many cluster-classes?
One per provider, version stays the same, version is increased on demand not with each k8s version.

Clusterclasses (very few, changed rarely):

• cluster-class-openstack-v1 (immutable, no renovate (of course)
• cluster-class-openstack-v2
• cluster-class-metal3-v1

Cluster-Addons (one per release+k8s combination):

• cluster-addon-openstack-v1.27
• cluster-addon-openstack-v1.28
• cluster-addon-openstack-v1.29

-> Change CSO-behaviour to read only clusterstackname from cluster.spec.topology.class and to read k8s version from cluster.spec.topology.version

Wishlist for the endresult:

• documentation page (One Page version, parsed out of each cluster-class?)
• tested clusterstacks (latest cluster-class version with 4 latest addons (k8s-version))
• renovate/dependabot updating stack-components

Start by reading issues #56, #96, and #101, then inspect the CSO behavior around cluster.spec.topology.class and cluster.spec.topology.version. Done means cluster-class names no longer encode Kubernetes versions, CSO reads the stack name and Kubernetes version separately, and the proposed cluster-class, addon, documentation, testing, and update workflows are addressed.