Port k3s external cloud controller docs

[brandond]

Content from https://docs.k3s.io/networking/networking-services#deploying-an-external-cloud-controller-manager needs to be made available in RKE2 docs. Should additionally suggest using HelmChart with bootstrap: true.

[om07github]

Hi @brandond 👋,

I'd like to work on this issue. I'll adapt the documentation content from the K3s site and add it to the RKE2 docs, along with a note recommending deployment via HelmChart with bootstrap: true. Please let me know if there’s a preferred section or format I should follow before I begin.

Thanks!