Provide variable fields from ClusterClass

[jschoone]

To make use of all possible variables provided by the specific ClusterClass, this should be generated out of it, the same way we do for the documentation, see SovereignCloudStack/cluster-stacks#94.
In case of moin cluster, they are available publicly available here

[mxmxchere]

Not only the variables can be fetched from the apiserver-link. The available cluster-classes and the namespaces they are deployed in can be used as input too.

[paulphys]

The new dynamic approach fetches all available ClusterClass definitions from the kubeapi-server of the moin-cluster via the REST API provided by capi-jsgen. The response is a JSON Schema object, which gets read by react-jsonschema-form to render the form. This new library allows us to dynamically render forms by providing a schema of the data and the associated UI components