🌱 Update examples & code snippets in Cluster API book to v1beta2 for ClusterClass

[sivchari]

What this PR does / why we need it:

Part of #12448

Which issue(s) this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close the issue(s) when PR gets merged):
Fixes #

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[fabriziopandini]

Thanks for this PR!
Could you kindly check the list of ClusterClass fields in https://main.cluster-api.sigs.k8s.io/tasks/experimental-features/cluster-class/change-clusterclass#effects-on-the-clusters (some of the fields name have been changed)

[sbueringer]

There are also some more changes coming in via: #12489, sorry.
(please check the diff in clusterclass_types.go)