Move k3s.cattle.io CR types to github.com/k3s-io/api

[brandond]

As part of rancher/rancher#44452 Rancher needs to import the ETCDSnapshotFile custom resource types in order to sync the custom resources, instead of syncing from the snapshot metadata configmap. They are currently unable to do this without pulling in other unwanted bits of K3s.

This was touched on as a possible necessity in the etcd snapshot metadata ADR:
https://github.com/k3s-io/k3s/blob/master/docs/adrs/etcd-snapshot-cr.md#existing-work

We should move the CR types out to a separate repo - I am proposing github.com/k3s-io/api to mirror how the Kubernetes project publishes their types at github.com/kubernetes/api. Note that we need to move all types in the apigroup together, so the Addon stub CR type will move as well.

[brandond]

Initial copy of APIs at https://github.com/k3s-io/api/tree/main, with a dependency on github.com/rancher/wrangler/v3. If we need to fork additional branches for older wrangler major versions we can do so.

Long term we should probably drop wrangler in favor of native controller-gen.

[brandond]

cc @jakefhyde