What is the minimum k8s version requirement?

### 🐛 Describe the bug

`
unknown field "x-kubernetes-validations" in io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1.JSONSchemaProps
`
k8s version:
`
Client Version: version.Info{Major:"1", Minor:"19", GitVersion:"v1.19.15", GitCommit:"58178e7f7aab455bc8de88d3bdd314b64141e7ee", GitTreeState:"clean", BuildDate:"2021-09-27T13:35:39Z", GoVersion:"go1.15.15", Compiler:"gc", Platform:"linux/amd64"}
Server Version: version.Info{Major:"1", Minor:"19", GitVersion:"v1.19.15", GitCommit:"58178e7f7aab455bc8de88d3bdd314b64141e7ee", GitTreeState:"clean", BuildDate:"2021-09-27T13:35:39Z", GoVersion:"go1.15.15", Compiler:"gc", Platform:"linux/amd64"}
`

### Steps to Reproduce

1.kubectl create -f https://github.com/vllm-project/aibrix/releases/download/v0.2.1/aibrix-dependency-v0.2.1.yaml
error occur:
```
namespace/envoy-gateway-system created
error: error validating "https://github.com/vllm-project/aibrix/releases/download/v0.2.1/aibrix-dependency-v0.2.1.yaml": error validating data: ValidationError(CustomResourceDefinition.spec.versions[0].schema.openAPIV3Schema.properties.spec.properties.sessionPersistence): unknown field "x-kubernetes-validations" in io.k8s.apiextensions-apiserver.pkg.apis.apiextensions.v1.JSONSchemaProps; if you choose to ignore these errors, turn validation off with --validate=false
```

### Expected behavior

work well

### Environment

v0.2.1