Adding Harvester Provider to the Cluster-API Provider section

[PatrickLaabs]

What would you like to be added (User Story)?

As a user, i was missing the Harvester Provider in the current list of available Providers on the Cluster API Book.

https://cluster-api.sigs.k8s.io/reference/providers

Based on the already merged PR #11653 we should add this Provider to the list 🥰

Detailed Description

Adding the Harvester Provider (https://github.com/rancher-sandbox/cluster-api-provider-harvester) to the List of infrastructure providers found here:

cluster-api/docs/book/src/reference/providers.md

Line 37 in cbd26f7

## Infrastructure

Anything else you would like to add?

No response

Label(s) to be applied

/kind feature
One or more /area label. See https://github.com/kubernetes-sigs/cluster-api/labels?q=area for the list of labels.

[k8s-ci-robot]

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