[cozystack-api] Fix updaing lists (#1171)

Signed-off-by: Andrei Kvapil <kvapss@gmail.com>

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## What this PR does

When you update lists in cozystack objects, you might face with the
error:

```
Warning: resource vminstances/mikrotik-demo is missing the kubectl.kubernetes.io/last-applied-configuration annotation which is required by kubectl apply. kubectl apply should only be used o
n resources created declaratively by either kubectl create --save-config or kubectl apply. The missing annotation will be patched automatically.
warning: error calculating patch from openapi v3 spec: unable to find api field "disks"
Error from server: error when applying patch:
{"metadata":{"annotations":{"kubectl.kubernetes.io/last-applied-configuration":"{\"apiVersion\":\"apps.cozystack.io/v1alpha1\",\"kind\":\"VMInstance\",\"metadata\":{\"annotations\":{},\"name
\":\"mikrotik-demo\",\"namespace\":\"tenant-vasya\"},\"spec\":{\"disks\":[{\"bus\":\"sata\",\"name\":\"mikrotik-system\"},{\"name\":\"mikrotik-iso\"}],\"instanceProfile\":\"ubuntu\",\"instan
ceType\":\"u1.medium\",\"running\":true}}\n"}},"spec":{"disks":[{"bus":"sata","name":"mikrotik-system"},{"name":"mikrotik-iso"}]}}
to:
Resource: "apps.cozystack.io/v1alpha1, Resource=vminstances", GroupVersionKind: "apps.cozystack.io/v1alpha1, Kind=VMInstance"
Name: "mikrotik-demo", Namespace: "tenant-vasya"
for: "/tmp/2": error when patching "/tmp/2": unable to find api field in struct JSON for the json field "disks"
```

This PR workarounds this.

Related to https://github.com/cozystack/cozystack/pull/1168

### Release note

<!--  Write a release note:
- Explain what has changed internally and for users.
- Start with the same [label] as in the PR title
- Follow the guidelines at
https://github.com/kubernetes/community/blob/master/contributors/guide/release-notes.md.
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```release-note
[cozystack-api] Fix updaing lists on cozystack objects
```

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Enhancements**
* Made resource specifications more flexible by allowing any content
under the specification property for dynamically registered resource
kinds.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

pkg/cmd/server/start.go

@@ -236,6 +236,15 @@ func (o *AppsServerOptions) Config() (*apiserver.Config, error) {
 				},
 			}
 
+			// make `.spec` schemaless so any keys are accepted
+			if specProp, ok := newDef.Properties["spec"]; ok {
+				specProp.AdditionalProperties = &spec.SchemaOrBool{
+					Allows: true,
+					Schema: &spec.Schema{},
+				}
+				newDef.Properties["spec"] = specProp
+			}
+
 			// 3. Save the new resource definition under the correct name
 			defs[resourceName] = *newDef
 			klog.V(6).Infof("PostProcessSpec: Added OpenAPI definition for %s\n", resourceName)