Document new schemebuilder patters in provider migration doc

Signed-off-by: Furkat Gofurov <furkat.gofurov@suse.com>

docs/book/src/developer/providers/migrations/v1.5-to-v1.6.md

@@ -31,3 +31,45 @@ maintainers of providers and consumers of our Go API.
 
 ### Suggested changes for providers
 
+- To enable clients to encode and decode your API, your types must be able to be registered within a  [scheme](https://pkg.go.dev/k8s.io/apimachinery/pkg/runtime#Scheme). The default kubebuilder scheme builder introduces a dependency on controller-runtime to your API types.
+
+  To mitigate it, Cluster API removed the reliance on controller-runtime scheme builder (see [#9045](https://github.com/kubernetes-sigs/cluster-api/pull/9045)) in order to reduce the number of dependancies being introcuded to its API types and make API types easily consumable by other projects.
+
+  E.g. now CAPI uses the following schemebuilder pattern:
+
+  ```diff
+  + metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+  + import "k8s.io/apimachinery/pkg/runtime"
+  - import "sigs.k8s.io/controller-runtime/pkg/scheme"
+
+  var (
+        // GroupVersion is group version used to register these objects.
+        ....
+
+  +     // schemeBuilder is used to add go types to the GroupVersionKind scheme.
+  +     schemeBuilder = runtime.NewSchemeBuilder(addKnownTypes)
+  -     // SchemeBuilder is used to add go types to the GroupVersionKind scheme.
+  -     SchemeBuilder = &scheme.Builder{GroupVersion: GroupVersion}
+
+        // AddToScheme adds the types in this group-version to the given scheme.
+  +     AddToScheme = schemeBuilder.AddToScheme
+  -     AddToScheme = SchemeBuilder.AddToScheme
+
+  +     objectTypes = []runtime.Object{}
+  )
+
+  + func addKnownTypes(scheme *runtime.Scheme) error {
+  +     scheme.AddKnownTypes(GroupVersion, objectTypes...)
+  +     metav1.AddToGroupVersion(scheme, GroupVersion)
+  +     return nil
+  + }
+  ```
+
+  and type registration:
+
+  ```diff
+  func init() {
+  +     objectTypes = append(objectTypes, &Captain{}, &CaptainList{})
+  -     SchemeBuilder.Register(&Captain{}, &CaptainList{})
+  }
+  ```