Deprecate obsolete errors pkg

The /errors package has its origin in when capi providers were machineActuators that needed to vendor core capi to function.
There's no usage recommendations and value is questionable since we moved to CRDs and conditions for interoperability between core and providers.
I think we should deprecate it and if there's any use case relying on it we should support it via conditions

docs/book/src/developer/providers/migrations/v1.8-to-v1.9.md

@@ -0,0 +1,22 @@
+# Cluster API v1.8 compared to v1.9
+
+This document provides an overview over relevant changes between Cluster API v1.8 and v1.9 for
+maintainers of providers and consumers of our Go API.
+
+## Go version
+
+- The Go version used by Cluster API is Go 1.22.x
+
+## Changes by Kind
+
+### Deprecation
+
+### Removals
+
+### API Changes
+
+### Other
+
+### Suggested changes for providers
+
+- The Errors package [has been deprecated in v1.8](https://github.com/kubernetes-sigs/cluster-api/issues/10784). It's recommented to remove any usage of the currently exported variables.

errors/doc.go

@@ -15,4 +15,6 @@ limitations under the License.
 */
 
 // Package errors makes a set of error message handlers available for use by Cluster API Providers.
+//
+// Deprecated: This package will be removed in one of the next releases.
 package errors