Decouple CRD generation to a separate repository

[Danil-Grigorev]

Currently we are generating rust CR definitions with kopium from the pulled manifests in the main repo. This is bad for several reasons:

• Unrelated API version diff introduced in random PR.
• Using main branch for CR version makes it non-backward compatible with previous CAPI versions. CRs need to be versioned together with upstream.
• We can’t establish automatic dependabot version bumps for the API package, as there is none ATM

To tackle this we can take approach taken by gateway-api with http://github.com/kube-rs/gateway-api-rs, and ask for addition of cluster-api CRDs into http://github.com/kube-rs/cluster-api-rs. This repository will automatically track cluster-api releases and update generated code per each new release.

Similar problems apply to Fleet CRDs, but the definitions there are not that frequent to update. In the meantime generation can be handled manually in the repo.

[Danil-Grigorev]

One interesting detail - with no much hassle this workflow in the kube-rs org can be adapted to fully automate new API releases coming from CAPI, with only added steps to generate the serde definitions within PR. Every other repo may then setup dependabot to bump API definitions coming from rust cluster-api repository.