fix description about custom resource (#9676)

Author: CaoShuFeng

content/en/docs/concepts/extend-kubernetes/api-extension/custom-resources.md

@@ -169,11 +169,11 @@ Aggregated APIs offer more advanced API features and customization of other feat
 
 | Feature | Description | CRDs | Aggregated API |
 | ------- | ----------- | ---- | -------------- |
-| Validation | Help users prevent errors and allow you to evolve your API independently of your clients. These features are most useful when there are many clients who can't all update at the same time. | Yes.  Most validation can be specified in the CRD using [OpenAPI v3.0 validation](/docs/tasks/access-kubernetes-api/extend-api-custom-resource-definitions/#validation).  Any other validations supported by addition of a Validating Webhook. | Yes, arbitrary validation checks |
-| Defaulting | See above | Yes, via a Mutating Webhook; Planned, via CRD OpenAPI schema. | Yes |
+| Validation | Help users prevent errors and allow you to evolve your API independently of your clients. These features are most useful when there are many clients who can't all update at the same time. | Yes.  Most validation can be specified in the CRD using [OpenAPI v3.0 validation](/docs/tasks/access-kubernetes-api/extend-api-custom-resource-definitions/#validation).  Any other validations supported by addition of a [Validating Webhook](/docs/reference/access-authn-authz/admission-controllers/#validatingadmissionwebhook-alpha-in-1-8-beta-in-1-9). | Yes, arbitrary validation checks |
+| Defaulting | See above | Yes, via a [Mutating Webhook](/docs/reference/access-authn-authz/admission-controllers/#mutatingadmissionwebhook-beta-in-1-9); Planned, via CRD OpenAPI schema. | Yes |
 | Multi-versioning | Allows serving the same object through two API versions. Can help ease API changes like renaming fields. Less important if you control your client versions. | No, but planned | Yes |
 | Custom Storage | If you need storage with a different performance mode (for example, time-series database instead of key-value store) or isolation for security (for example, encryption secrets or different | No | Yes |
-| Custom Business Logic | Perform arbitrary checks or actions when creating, reading, updating or deleting an object | Yes, using Webhooks. | Yes |
+| Custom Business Logic | Perform arbitrary checks or actions when creating, reading, updating or deleting an object | Yes, using [Webhooks](/docs/reference/access-authn-authz/extensible-admission-controllers/#admission-webhooks). | Yes |
 | Scale Subresource | Allows systems like HorizontalPodAutoscaler and PodDisruptionBudget interact with your new resource | [Yes](https://kubernetes.io/docs/tasks/access-kubernetes-api/extend-api-custom-resource-definitions/#scale-subresource)  | Yes |
 | Status Subresource | <ul><li>Finer-grained access control: user writes spec section, controller writes status section.</li><li>Allows incrementing object Generation on custom resource data mutation (requires separate spec and status sections in the resource)</li></ul> | [Yes](https://kubernetes.io/docs/tasks/access-kubernetes-api/extend-api-custom-resource-definitions/#status-subresource) | Yes |
 | Other Subresources | Add operations other than CRUD, such as "logs" or "exec". | No | Yes |