Refactor as a Crossplane Provider

[lmakarov]

In light of #14, Crossplane could be a solid foundation for kubeflare.

Crossplane is FOSS and has a provider-template repo to kickstart a new provider integration.

[diamonwiggins]

Will definitely consider this. Haven't spent any time working with Crossplane yet, but from the little I do know I can definitely see the overlap. One thing we've discussed doing with this project, similar to https://github.com/kubernetes-sigs/external-dns, is adding the ability to watch an Ingress resource and create Cloudflare DNS records from them. Will keep this open until we make a decision here to allow for further discussion.