bug: cannot handle CRDs with multiple versions

[embik]

Describe the bug

It seems that we cannot publish resources (via PublishedResources) for CRDs with multiple versions in the CRD. That obviously shouldn't be the case.

The error message in question is:

{"level":"error","time":"2025-02-06T17:39:01.145Z","caller":"controller/controller.go:263","msg":"Reconciler error","controller":"syncagent-apiresourceschema","controllerGroup":"syncagent.kcp.io","controllerKind":"PublishedResource","PublishedResource":{"name":"published-resource-name"},"namespace":"","name":"published-resource-name","reconcileID":"f1fea0dc-4568-4149-8943-694fe567eab5", "error":"failed to create APIResourceSchema: APIResourceSchema.apis.kcp.io \"v4577dd55.<resource>\" is invalid: spec: Invalid value: \"object\": Conversion must be specified when multiple versions exist"}

Steps To Reproduce

1. Create CRD with multiple versions.
2. Publish it.
3. See api-syncagent fail.

Expected Behaviour

We should select the actively served version and publish that.

Additional Context

No response